Inline documentation for hooks in wp-admin/edit-tags.php.

Props pauldewouters for the initial patch.
Fixes #25532.

Built from https://develop.svn.wordpress.org/trunk@26274


git-svn-id: http://core.svn.wordpress.org/trunk@26179 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Widgets:
- Remove the !important styles that were overriding the widget width when expanded.
- Fix missing border-bottom from widgets when dragged and expanded.
Props shaunandrews, see #26117.
Built from https://develop.svn.wordpress.org/trunk@26275


git-svn-id: http://core.svn.wordpress.org/trunk@26180 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Heartbeat: use cached $document instead of $(document), props TobiasBg, see #25073
Built from https://develop.svn.wordpress.org/trunk@26276


git-svn-id: http://core.svn.wordpress.org/trunk@26181 1a063a9b-81f0-0310-95a4-ce76da25c4cd