Heartbeat: rename some vars/args to make them more intuitive, don't set user_id on every request, see #23216

git-svn-id: http://core.svn.wordpress.org/trunk@24406 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Compress scripts/styles: 3.6-beta3-24407.

git-svn-id: http://core.svn.wordpress.org/trunk@24407 1a063a9b-81f0-0310-95a4-ce76da25c4cd