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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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
Edit image modal: check if full size exists before trying to use it for setting aspect ratio, props gcorne, see #27366
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TinyMCE: update the default style for html5-captions, props obenland fixes #26642
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Throw a user notice when the editor ID used for TinyMCE contains brackets, props nacin, fixes #27601 
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When autosaving a new post for the first time after a title was typed, cancel the autosave if the user is submitting the form. (Includes a precommit fix for customize-controls.css.) Props Nessworthy, davidmarichal, fixes #27657
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Fix a typo in the PHPDoc description for the `WP_Http_Curl->max_body_length` property.

Props eightface.
Fixes #27681.

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