Post locks: make sure we never overwrite a draft when it's locked, clean up wp_ajax_autosave() and make wp-refresh-post-lock a bit more robust, see #23697

git-svn-id: http://core.svn.wordpress.org/trunk@23981 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Fix accidental revert of revisions comparison in [23981] 

git-svn-id: http://core.svn.wordpress.org/trunk@23982 1a063a9b-81f0-0310-95a4-ce76da25c4cd