Add unit tests to confirm that --- is properly converted to — by wptexturize() where appropriate.

Props miqrogroove.
Fixes #28483.

Built from https://develop.svn.wordpress.org/trunk@28763


git-svn-id: http://core.svn.wordpress.org/trunk@28576 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/formatting.php

@@ -274,6 +274,8 @@ function _wptexturize_pushpop_element($text, &$stack, $disabled_elements, $openi
 
 			array_push($stack, $matches[1]);
 		}
+	} elseif ( 0 == count( $stack ) ) {
+		// Stack is empty. Just stop.
 	} else {
 		// Closing? Check $text+2 against disabled elements
 		$c = preg_quote($closing, '/');