Adds WP_Customize_Setting->sanitize_js_callback and 'customize_sanitize_js_$settingID' filter, to filter values before they're passed to JS using WP_Customize_Setting->js_value().
Adds support for regular hex colors to the color picker.
Changes color methods:
* sanitize_hex_color() accepts 3 and 6 digit hex colors (with hashes) and the empty string.
* sanitize_hex_color_no_hash() accepts 3 and 6 digit hex colors (without hashes) and the empty string.
* maybe_hash_hex_color() ensures that a hex color has a hash, and otherwise leaves the value untouched.
git-svn-id: http://core.svn.wordpress.org/trunk@20936 1a063a9b-81f0-0310-95a4-ce76da25c4cd