diff --git a/wp-admin/includes/ajax-actions.php b/wp-admin/includes/ajax-actions.php
index ecca65ad32..289d959224 100644
--- a/wp-admin/includes/ajax-actions.php
+++ b/wp-admin/includes/ajax-actions.php
@@ -1165,7 +1165,7 @@ function wp_ajax_add_menu_item() {
 	/** This filter is documented in wp-admin/includes/nav-menu.php */
 	$walker_class_name = apply_filters( 'wp_edit_nav_menu_walker', 'Walker_Nav_Menu_Edit', $_POST['menu'] );
 
-	if ( ! class_exists( $walker_class_name ) )
+	if ( ! class_exists( $walker_class_name, false ) )
 		wp_die( 0 );
 
 	if ( ! empty( $menu_items ) ) {
diff --git a/wp-admin/includes/deprecated.php b/wp-admin/includes/deprecated.php
index d984bdbe92..7e37a3b7b6 100644
--- a/wp-admin/includes/deprecated.php
+++ b/wp-admin/includes/deprecated.php
@@ -316,7 +316,7 @@ function get_nonauthor_user_ids() {
 	return $wpdb->get_col( $wpdb->prepare("SELECT user_id FROM $wpdb->usermeta WHERE meta_key = %s AND meta_value = '0'", $level_key) );
 }
 
-if ( !class_exists('WP_User_Search') ) :
+if ( ! class_exists( 'WP_User_Search', false ) ) :
 /**
  * WordPress User Search class.
  *
@@ -757,7 +757,7 @@ function wp_tiny_mce( $teeny = false, $settings = false ) {
 
 	static $num = 1;
 
-	if ( ! class_exists('_WP_Editors' ) )
+	if ( ! class_exists( '_WP_Editors', false ) )
 		require_once( ABSPATH . WPINC . '/class-wp-editor.php' );
 
 	$editor_id = 'content' . $num++;
diff --git a/wp-admin/includes/file.php b/wp-admin/includes/file.php
index 8fc0fe1205..62b644be3a 100644
--- a/wp-admin/includes/file.php
+++ b/wp-admin/includes/file.php
@@ -559,7 +559,7 @@ function unzip_file($file, $to) {
 	 *
 	 * @param bool $ziparchive Whether to use ZipArchive. Default true.
 	 */
-	if ( class_exists( 'ZipArchive' ) && apply_filters( 'unzip_file_use_ziparchive', true ) ) {
+	if ( class_exists( 'ZipArchive', false ) && apply_filters( 'unzip_file_use_ziparchive', true ) ) {
 		$result = _unzip_file_ziparchive($file, $to, $needed_dirs);
 		if ( true === $result ) {
 			return $result;
@@ -848,7 +848,7 @@ function WP_Filesystem( $args = false, $context = false, $allow_relaxed_file_own
 	if ( ! $method )
 		return false;
 
-	if ( ! class_exists("WP_Filesystem_$method") ) {
+	if ( ! class_exists( "WP_Filesystem_$method", false  ) ) {
 
 		/**
 		 * Filter the path for a specific filesystem method class file.
diff --git a/wp-admin/includes/media.php b/wp-admin/includes/media.php
index 7b803bb132..63018fc69f 100644
--- a/wp-admin/includes/media.php
+++ b/wp-admin/includes/media.php
@@ -2974,7 +2974,7 @@ function wp_read_video_metadata( $file ) {
 
 	$metadata = array();
 
-	if ( ! class_exists( 'getID3' ) )
+	if ( ! class_exists( 'getID3', false ) )
 		require( ABSPATH . WPINC . '/ID3/getid3.php' );
 	$id3 = new getID3();
 	$data = $id3->analyze( $file );
@@ -3029,7 +3029,7 @@ function wp_read_audio_metadata( $file ) {
 		return false;
 	$metadata = array();
 
-	if ( ! class_exists( 'getID3' ) )
+	if ( ! class_exists( 'getID3', false ) )
 		require( ABSPATH . WPINC . '/ID3/getid3.php' );
 	$id3 = new getID3();
 	$data = $id3->analyze( $file );
diff --git a/wp-admin/includes/misc.php b/wp-admin/includes/misc.php
index d65d22b2d7..454c68647a 100644
--- a/wp-admin/includes/misc.php
+++ b/wp-admin/includes/misc.php
@@ -454,8 +454,9 @@ function set_screen_options() {
 function iis7_rewrite_rule_exists($filename) {
 	if ( ! file_exists($filename) )
 		return false;
-	if ( ! class_exists('DOMDocument') )
+	if ( ! class_exists( 'DOMDocument', false ) ) {
 		return false;
+	}
 
 	$doc = new DOMDocument();
 	if ( $doc->load($filename) === false )
@@ -481,8 +482,9 @@ function iis7_delete_rewrite_rule($filename) {
 	if ( ! file_exists($filename) )
 		return true;
 
-	if ( ! class_exists('DOMDocument') )
+	if ( ! class_exists( 'DOMDocument', false ) ) {
 		return false;
+	}
 
 	$doc = new DOMDocument();
 	$doc->preserveWhiteSpace = false;
@@ -511,8 +513,9 @@ function iis7_delete_rewrite_rule($filename) {
  * @return bool
  */
 function iis7_add_rewrite_rule($filename, $rewrite_rule) {
-	if ( ! class_exists('DOMDocument') )
+	if ( ! class_exists( 'DOMDocument', false ) ) {
 		return false;
+	}
 
 	// If configuration file does not exist then we create one.
 	if ( ! file_exists($filename) ) {
diff --git a/wp-admin/includes/nav-menu.php b/wp-admin/includes/nav-menu.php
index aa235cf4a0..e557dd04ac 100644
--- a/wp-admin/includes/nav-menu.php
+++ b/wp-admin/includes/nav-menu.php
@@ -875,7 +875,7 @@ function wp_get_nav_menu_to_edit( $menu_id = 0 ) {
 		 */
 		$walker_class_name = apply_filters( 'wp_edit_nav_menu_walker', 'Walker_Nav_Menu_Edit', $menu_id );
 
-		if ( class_exists( $walker_class_name ) )
+		if ( class_exists( $walker_class_name, false ) )
 			$walker = new $walker_class_name;
 		else
 			return new WP_Error( 'menu_walker_not_exist', sprintf( __('The Walker class named <strong>%s</strong> does not exist.'), $walker_class_name ) );
diff --git a/wp-admin/includes/template-functions.php b/wp-admin/includes/template-functions.php
index 82614ebe76..4d8b667558 100644
--- a/wp-admin/includes/template-functions.php
+++ b/wp-admin/includes/template-functions.php
@@ -1910,7 +1910,7 @@ function _wp_admin_html_begin() {
  * @return WP_Screen Screen object.
  */
 function convert_to_screen( $hook_name ) {
-	if ( ! class_exists( 'WP_Screen' ) ) {
+	if ( ! class_exists( 'WP_Screen', false ) ) {
 		_doing_it_wrong( 'convert_to_screen(), add_meta_box()', __( "Likely direct inclusion of wp-admin/includes/template.php in order to use add_meta_box(). This is very wrong. Hook the add_meta_box() call into the add_meta_boxes action instead." ), '3.3' );
 		return (object) array( 'id' => '_invalid', 'base' => '_are_belong_to_us' );
 	}
diff --git a/wp-includes/admin-bar.php b/wp-includes/admin-bar.php
index 8a1a2be301..a12e9c9e71 100644
--- a/wp-includes/admin-bar.php
+++ b/wp-includes/admin-bar.php
@@ -37,7 +37,7 @@ function _wp_admin_bar_init() {
 	 * @param string $wp_admin_bar_class Admin bar class to use. Default 'WP_Admin_Bar'.
 	 */
 	$admin_bar_class = apply_filters( 'wp_admin_bar_class', 'WP_Admin_Bar' );
-	if ( class_exists( $admin_bar_class ) )
+	if ( class_exists( $admin_bar_class, false ) )
 		$wp_admin_bar = new $admin_bar_class;
 	else
 		return false;
diff --git a/wp-includes/class-feed.php b/wp-includes/class-feed.php
index 6e109e1616..919440f18e 100644
--- a/wp-includes/class-feed.php
+++ b/wp-includes/class-feed.php
@@ -1,6 +1,6 @@
 <?php
 
-if ( !class_exists('SimplePie') )
+if ( ! class_exists( 'SimplePie', false ) )
 	require_once( ABSPATH . WPINC . '/class-simplepie.php' );
 
 class WP_Feed_Cache extends SimplePie_Cache {
diff --git a/wp-includes/class-oembed.php b/wp-includes/class-oembed.php
index 35f74a723c..f2262c5b1f 100644
--- a/wp-includes/class-oembed.php
+++ b/wp-includes/class-oembed.php
@@ -489,7 +489,7 @@ class WP_oEmbed {
 	 * @return object|false
 	 */
 	private function _parse_xml_body( $response_body ) {
-		if ( ! function_exists( 'simplexml_import_dom' ) || ! class_exists( 'DOMDocument' ) )
+		if ( ! function_exists( 'simplexml_import_dom' ) || ! class_exists( 'DOMDocument', false ) )
 			return false;
 
 		$dom = new DOMDocument;
diff --git a/wp-includes/class-simplepie.php b/wp-includes/class-simplepie.php
index 64f9fa9be4..958ba463e9 100644
--- a/wp-includes/class-simplepie.php
+++ b/wp-includes/class-simplepie.php
@@ -1,5 +1,5 @@
 <?php
-if ( ! class_exists( 'SimplePie' ) ) :
+if ( ! class_exists( 'SimplePie', false ) ) :
 
 // Load classes we will need.
 require ABSPATH . WPINC . '/SimplePie/Misc.php';
diff --git a/wp-includes/class-snoopy.php b/wp-includes/class-snoopy.php
index f9db055db4..e08e732157 100644
--- a/wp-includes/class-snoopy.php
+++ b/wp-includes/class-snoopy.php
@@ -5,7 +5,7 @@
  */
 _deprecated_file( basename( __FILE__ ), '3.0', WPINC . '/http.php' );
 
-if ( !class_exists( 'Snoopy' ) ) :
+if ( ! class_exists( 'Snoopy', false ) ) :
 /*************************************************
 
 Snoopy - the PHP net client
diff --git a/wp-includes/class-wp-image-editor-imagick.php b/wp-includes/class-wp-image-editor-imagick.php
index bcfb576433..0c1cd08a60 100644
--- a/wp-includes/class-wp-image-editor-imagick.php
+++ b/wp-includes/class-wp-image-editor-imagick.php
@@ -48,7 +48,7 @@ class WP_Image_Editor_Imagick extends WP_Image_Editor {
 	public static function test( $args = array() ) {
 
 		// First, test Imagick's extension and classes.
-		if ( ! extension_loaded( 'imagick' ) || ! class_exists( 'Imagick' ) || ! class_exists( 'ImagickPixel' ) )
+		if ( ! extension_loaded( 'imagick' ) || ! class_exists( 'Imagick', false ) || ! class_exists( 'ImagickPixel', false ) )
 			return false;
 
 		if ( version_compare( phpversion( 'imagick' ), '2.2.0', '<' ) )
diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index ef2976c75c..a27502360a 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -3690,7 +3690,7 @@ function iis7_supports_permalinks() {
 		 * Lastly we make sure that PHP is running via FastCGI. This is important because if it runs
 		 * via ISAPI then pretty permalinks will not work.
 		 */
-		$supports_permalinks = class_exists('DOMDocument') && isset($_SERVER['IIS_UrlRewriteModule']) && ( PHP_SAPI == 'cgi-fcgi' );
+		$supports_permalinks = class_exists( 'DOMDocument', false ) && isset($_SERVER['IIS_UrlRewriteModule']) && ( PHP_SAPI == 'cgi-fcgi' );
 	}
 
 	/**
diff --git a/wp-includes/general-template.php b/wp-includes/general-template.php
index eb3b8912e6..3d437ed024 100644
--- a/wp-includes/general-template.php
+++ b/wp-includes/general-template.php
@@ -2580,7 +2580,7 @@ function wp_default_editor() {
  * @param array  $settings  See _WP_Editors::editor().
  */
 function wp_editor( $content, $editor_id, $settings = array() ) {
-	if ( ! class_exists( '_WP_Editors' ) )
+	if ( ! class_exists( '_WP_Editors', false ) )
 		require( ABSPATH . WPINC . '/class-wp-editor.php' );
 
 	_WP_Editors::editor($content, $editor_id, $settings);
diff --git a/wp-includes/pluggable-deprecated.php b/wp-includes/pluggable-deprecated.php
index e63036af10..39fcd49d98 100644
--- a/wp-includes/pluggable-deprecated.php
+++ b/wp-includes/pluggable-deprecated.php
@@ -178,7 +178,7 @@ endif;
  *
  * @link https://wordpress.org/plugins/atom-publishing-protocol/
  */
-if ( ! class_exists( 'wp_atom_server' ) ) {
+if ( ! class_exists( 'wp_atom_server', false ) ) {
 	class wp_atom_server {
 		public function __call( $name, $arguments ) {
 			_deprecated_function( __CLASS__ . '::' . $name, '3.5', 'the Atom Publishing Protocol plugin' );
diff --git a/wp-includes/pluggable.php b/wp-includes/pluggable.php
index afccae9367..d58f18940b 100644
--- a/wp-includes/pluggable.php
+++ b/wp-includes/pluggable.php
@@ -2387,7 +2387,7 @@ function wp_text_diff( $left_string, $right_string, $args = null ) {
 	$defaults = array( 'title' => '', 'title_left' => '', 'title_right' => '' );
 	$args = wp_parse_args( $args, $defaults );
 
-	if ( !class_exists( 'WP_Text_Diff_Renderer_Table' ) )
+	if ( ! class_exists( 'WP_Text_Diff_Renderer_Table', false ) )
 		require( ABSPATH . WPINC . '/wp-diff.php' );
 
 	$left_string  = normalize_whitespace($left_string);
diff --git a/wp-includes/pomo/entry.php b/wp-includes/pomo/entry.php
index ca706fca16..67f6719b2b 100644
--- a/wp-includes/pomo/entry.php
+++ b/wp-includes/pomo/entry.php
@@ -7,7 +7,7 @@
  * @subpackage entry
  */
 
-if ( !class_exists( 'Translation_Entry' ) ):
+if ( ! class_exists( 'Translation_Entry', false ) ):
 /**
  * Translation_Entry class encapsulates a translatable string
  */
diff --git a/wp-includes/pomo/mo.php b/wp-includes/pomo/mo.php
index 1757061960..164c6c9ccd 100644
--- a/wp-includes/pomo/mo.php
+++ b/wp-includes/pomo/mo.php
@@ -10,7 +10,7 @@
 require_once dirname(__FILE__) . '/translations.php';
 require_once dirname(__FILE__) . '/streams.php';
 
-if ( !class_exists( 'MO' ) ):
+if ( ! class_exists( 'MO', false ) ):
 class MO extends Gettext_Translations {
 
 	var $_nplurals = 2;
diff --git a/wp-includes/pomo/po.php b/wp-includes/pomo/po.php
index 381977c5cf..f8933d2cd8 100644
--- a/wp-includes/pomo/po.php
+++ b/wp-includes/pomo/po.php
@@ -16,7 +16,7 @@ ini_set('auto_detect_line_endings', 1);
 /**
  * Routines for working with PO files
  */
-if ( !class_exists( 'PO' ) ):
+if ( ! class_exists( 'PO', false ) ):
 class PO extends Gettext_Translations {
 
 	var $comments_before_headers = '';
@@ -355,7 +355,7 @@ class PO extends Gettext_Translations {
 	/**
 	 * @staticvar string   $last_line
 	 * @staticvar boolean  $use_last_line
-	 * 
+	 *
 	 * @param     resource $f
 	 * @param     string   $action
 	 * @return boolean
diff --git a/wp-includes/pomo/streams.php b/wp-includes/pomo/streams.php
index 1b6b2282bb..8373295feb 100644
--- a/wp-includes/pomo/streams.php
+++ b/wp-includes/pomo/streams.php
@@ -8,7 +8,7 @@
  * @subpackage streams
  */
 
-if ( !class_exists( 'POMO_Reader' ) ):
+if ( ! class_exists( 'POMO_Reader', false ) ):
 class POMO_Reader {
 
 	var $endian = 'little';
@@ -134,7 +134,7 @@ class POMO_Reader {
 }
 endif;
 
-if ( !class_exists( 'POMO_FileReader' ) ):
+if ( ! class_exists( 'POMO_FileReader', false ) ):
 class POMO_FileReader extends POMO_Reader {
 
 	/**
@@ -204,7 +204,7 @@ class POMO_FileReader extends POMO_Reader {
 }
 endif;
 
-if ( !class_exists( 'POMO_StringReader' ) ):
+if ( ! class_exists( 'POMO_StringReader', false ) ):
 /**
  * Provides file-like methods for manipulating a string instead
  * of a physical file.
@@ -267,7 +267,7 @@ class POMO_StringReader extends POMO_Reader {
 }
 endif;
 
-if ( !class_exists( 'POMO_CachedFileReader' ) ):
+if ( ! class_exists( 'POMO_CachedFileReader', false ) ):
 /**
  * Reads the contents of the file in the beginning.
  */
@@ -292,7 +292,7 @@ class POMO_CachedFileReader extends POMO_StringReader {
 }
 endif;
 
-if ( !class_exists( 'POMO_CachedIntFileReader' ) ):
+if ( ! class_exists( 'POMO_CachedIntFileReader', false ) ):
 /**
  * Reads the contents of the file in the beginning.
  */
diff --git a/wp-includes/pomo/translations.php b/wp-includes/pomo/translations.php
index 8db80c85a6..6008f4aa18 100644
--- a/wp-includes/pomo/translations.php
+++ b/wp-includes/pomo/translations.php
@@ -9,7 +9,7 @@
 
 require_once dirname(__FILE__) . '/entry.php';
 
-if ( !class_exists( 'Translations' ) ):
+if ( ! class_exists( 'Translations', false ) ):
 class Translations {
 	var $entries = array();
 	var $headers = array();
@@ -272,7 +272,7 @@ class Gettext_Translations extends Translations {
 }
 endif;
 
-if ( !class_exists( 'NOOP_Translations' ) ):
+if ( ! class_exists( 'NOOP_Translations', false ) ):
 /**
  * Provides the same interface as Translations, but doesn't do anything
  */
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 293b0c2df6..6f56814492 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34347';
+$wp_version = '4.4-alpha-34348';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-includes/wp-db.php b/wp-includes/wp-db.php
index a0c59cfc35..c745cb2430 100644
--- a/wp-includes/wp-db.php
+++ b/wp-includes/wp-db.php
@@ -2993,10 +2993,11 @@ class wpdb {
 	 */
 	public function bail( $message, $error_code = '500' ) {
 		if ( !$this->show_errors ) {
-			if ( class_exists( 'WP_Error' ) )
+			if ( class_exists( 'WP_Error', false ) ) {
 				$this->error = new WP_Error($error_code, $message);
-			else
+			} else {
 				$this->error = $message;
+			}
 			return false;
 		}
 		wp_die($message);
diff --git a/wp-includes/wp-diff.php b/wp-includes/wp-diff.php
index 1e8fc0e921..832a62f8b3 100644
--- a/wp-includes/wp-diff.php
+++ b/wp-includes/wp-diff.php
@@ -8,7 +8,7 @@
  * @subpackage Diff
  */
 
-if ( !class_exists( 'Text_Diff' ) ) {
+if ( ! class_exists( 'Text_Diff', false ) ) {
 	/** Text_Diff class */
 	require( dirname(__FILE__).'/Text/Diff.php' );
 	/** Text_Diff_Renderer class */