Add is_customize_preview(), a conditional function to check if the site is being previewed in the Customizer.

props sammybeats, mattwiebe.
fixes #23509.
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git-svn-id: http://core.svn.wordpress.org/trunk@28787 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Fix a regression of positioning in Attachment Display Settings.

props paulwilde.
see #24716.
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git-svn-id: http://core.svn.wordpress.org/trunk@28788 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Fix alignment of Advanced Options close toggle arrow in Edit Media dialog.

props paulwilde.
fixes #28752.
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git-svn-id: http://core.svn.wordpress.org/trunk@28789 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Reinstate 'install_themes_tabs' filter.

props ghost1227.
fixes #28578.
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git-svn-id: http://core.svn.wordpress.org/trunk@28790 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add 'status-sticky' class in get_post_class() for sticky posts in the admin.

props mordauk, netweb.
fixes #22590.
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git-svn-id: http://core.svn.wordpress.org/trunk@28791 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove debug remnants, see #28595
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git-svn-id: http://core.svn.wordpress.org/trunk@28792 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Don't include plugin.php twice in setup-config.php.

fixes #28744. see #28740, [28978].

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git-svn-id: http://core.svn.wordpress.org/trunk@28793 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Bring the language chooser to setup-config.php.

see #28577.

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git-svn-id: http://core.svn.wordpress.org/trunk@28794 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Introduce wp_dropdown_languages() and use it on general settings.

Early rough cut. Obviously not fully implemented.

see #15677.

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git-svn-id: http://core.svn.wordpress.org/trunk@28795 1a063a9b-81f0-0310-95a4-ce76da25c4cd