TinyMCE help modal:
- Don't load the old tiny_mce_popup.js.
- Add the shortcut for <code> and the second shortcut for link to the shortcuts listing.
- Update some of the text.
See #27100
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git-svn-id: http://core.svn.wordpress.org/trunk@27857 1a063a9b-81f0-0310-95a4-ce76da25c4cd