Create one autosave per user rather than a single autosave for all users. Remove unused code from autosave.js and wp_ajax_autosave(). See #23665.

git-svn-id: http://core.svn.wordpress.org/trunk@23735 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Compress scripts/styles: 3.6-alpha-23736.

git-svn-id: http://core.svn.wordpress.org/trunk@23736 1a063a9b-81f0-0310-95a4-ce76da25c4cd