Update MediaElement.js to a new 2.12.1 (untagged) build. see #24183.



git-svn-id: http://core.svn.wordpress.org/trunk@24786 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Autosave: Don't save an autosave unnecessarily when the post editor loads and TinyMCE is the default editor.

Delete such useless autosaves when we detect them in edit-form-advanced.php.

see #7392.



git-svn-id: http://core.svn.wordpress.org/trunk@24787 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove curly quotes from auto content generation for audio tracks on upload. Texturize should be doing this on display.

props tollmanz.
fixes 24810.



git-svn-id: http://core.svn.wordpress.org/trunk@24788 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Fix some sizing issues with video embeds, and improve video/audio embed shortcode flexibility.

* `loop`, `autoplay`, and `preload` are now available via the shortcode. Use them non-annoyingly, please!
* Attributes that pass through the filters are now proper key/value pairs, not an array of `key="value"` strings.
* `preload` defaults to `metadata` for videos. This fixes the vertical video preview and Safari ogv/webm playback issues.
* Wrap a div around video embeds to combat a ME.js issue with responsive width=100% themes. Props kovshenin.

Fixes #24134, #24798.

git-svn-id: http://core.svn.wordpress.org/trunk@24789 1a063a9b-81f0-0310-95a4-ce76da25c4cd