Theme Installer: Center spinner, remove plural string.

fixes #27581. see #27055.

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git-svn-id: http://core.svn.wordpress.org/trunk@27770 1a063a9b-81f0-0310-95a4-ce76da25c4cd
TinyMCE: better calculation for editor height when switching Text to Visual and back. Add stopping of editor resizing when the mouse leaves the browser window. See #27279
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git-svn-id: http://core.svn.wordpress.org/trunk@27771 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Edit image modal:
- Make the calculation of the aspect ratio more robust.
- Better getting of the image height and width.
Props gcorne, see #27366
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git-svn-id: http://core.svn.wordpress.org/trunk@27772 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove a blank line and @global reference in the PHPDoc for `comment_author_email_link()`.

Props norcross, ocean90.
Fixes #27655.

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git-svn-id: http://core.svn.wordpress.org/trunk@27773 1a063a9b-81f0-0310-95a4-ce76da25c4cd
TinyMCE: add image backgrounds for more and nextpage tags (also jshint fix for theme.js). Fixes #27106
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git-svn-id: http://core.svn.wordpress.org/trunk@27774 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add missing space between strings.

props rachelbaker.
fixes #27597.

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git-svn-id: http://core.svn.wordpress.org/trunk@27775 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Header images: Handle cropping failures.

props ehg.
see #21785.

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git-svn-id: http://core.svn.wordpress.org/trunk@27776 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Header images: Accessibility and style improvements. Headers no longer jump around when chosen.

props mcsf, ehg.
see #21785.

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git-svn-id: http://core.svn.wordpress.org/trunk@27777 1a063a9b-81f0-0310-95a4-ce76da25c4cd