Revisions UI: Add a help tab. props siobhan, DrewAPicture. see #23899.

git-svn-id: http://core.svn.wordpress.org/trunk@24173 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Revisions UI: Just another update - Now with improved tick marks and tooltips.

props adamsilverstein. see #23935.

git-svn-id: http://core.svn.wordpress.org/trunk@24174 1a063a9b-81f0-0310-95a4-ce76da25c4cd