Plupload wrapper: Call init callback on PostInit event.
Fixes the background image uploader in Customizer, which was broken after [27316].

fixes #27620.
Built from https://develop.svn.wordpress.org/trunk@27933


git-svn-id: http://core.svn.wordpress.org/trunk@27763 1a063a9b-81f0-0310-95a4-ce76da25c4cd
TinyMCE: improve setting disabled/enabled/activated states on the Unlink button, fixes #27309
Built from https://develop.svn.wordpress.org/trunk@27934


git-svn-id: http://core.svn.wordpress.org/trunk@27764 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Database: Fall back from ext/mysqli to ext/mysql if the connection fails.

This allows us to avoid breaking a site that works under ext/mysql but is misconfigured for ext/mysqli.

props pento.
see #21663.

Built from https://develop.svn.wordpress.org/trunk@27935


git-svn-id: http://core.svn.wordpress.org/trunk@27765 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Themes: Hide 'Add New' with no JS. see #27055.

Built from https://develop.svn.wordpress.org/trunk@27936


git-svn-id: http://core.svn.wordpress.org/trunk@27766 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Theme Installer: Fix sorting, counts, keyboard navigation; add prev/next to previews.

props matveb.
see #27055.

Built from https://develop.svn.wordpress.org/trunk@27937


git-svn-id: http://core.svn.wordpress.org/trunk@27767 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Fix typo in verify_file_md5() description. see [25541].

props siobhan.
see #27651.
Built from https://develop.svn.wordpress.org/trunk@27938


git-svn-id: http://core.svn.wordpress.org/trunk@27768 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Clarify tooltips on Edit Image screen.

props siobhan.
fixes #27651.
Built from https://develop.svn.wordpress.org/trunk@27939


git-svn-id: http://core.svn.wordpress.org/trunk@27769 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Theme Installer: Center spinner, remove plural string.

fixes #27581. see #27055.

Built from https://develop.svn.wordpress.org/trunk@27940


git-svn-id: http://core.svn.wordpress.org/trunk@27770 1a063a9b-81f0-0310-95a4-ce76da25c4cd