* When you scroll down the diff view, the controls will pin to the top.
* The revisions meta view was cleaned up. Copy changes.
* Loading indicator in the center of the screen (so it follows as you scroll).
* Tooltips "flip" when you cross the center line, so that they don't hit the container edge and wrap for later revisions.
* The "Restore" button's inactive state is handled on render, instead of after.
* Make sure we always have a current revision, even if the timestamp doesn't work out on the most recent one.
See #24804. Props markjaquith, nacin, ocean90, aaroncampbell.
git-svn-id: https://develop.svn.wordpress.org/trunk@24761 602fd350-edb4-49c9-b593-d223f7449a82
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