Prompt the user before leaving the Customizer if they have unsaved changes. props westonruter. fixes #25439.

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git-svn-id: http://core.svn.wordpress.org/trunk@28813 1a063a9b-81f0-0310-95a4-ce76da25c4cd
When accessing the Customizer from the admin menu, make sure the user is returned to the originating page upon close. We should still investigate the general usage of `customize-loader.js` moving forward, but this approach fixes the immediate issue. props westonruter. fixes #25457.

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git-svn-id: http://core.svn.wordpress.org/trunk@28814 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Allow an `array()` to be passed as the value for `orderby` to `WP_Query`. Allows for an independent `order` value for each key.

Example: `'orderby' => array( 'title' => 'DESC', 'menu_order' => 'ASC' )`.

Adds docs and unit tests.

Props wonderboymusic, johnbillion, DrewAPicture, dd32, andy.
See #17065.

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git-svn-id: http://core.svn.wordpress.org/trunk@28815 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Use wp_hash() instead of AUTH_KEY in WP_Customize_Widgets::get_instance_hash_key().

props juliobox.
fixes #28783.
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git-svn-id: http://core.svn.wordpress.org/trunk@28816 1a063a9b-81f0-0310-95a4-ce76da25c4cd
When setting the poster image for a video shortcode, set that image as the featured image for that attachment (if found) in the background. This AJAX functionality could be used for audio as well.

Introduces `attachment_url_to_postid()` to attempt to turn URLs into post IDs.

Fixes #27891.

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git-svn-id: http://core.svn.wordpress.org/trunk@28817 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Implement email and url input types where appropriate. Props Kau-Boy. Fixes #22183.
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git-svn-id: http://core.svn.wordpress.org/trunk@28818 1a063a9b-81f0-0310-95a4-ce76da25c4cd