'DiffRevisionTools': Override or extend the revision tools available from the
diff view, i.e. undo, etc.
-$rev: Revision object
+$newRev: Revision object of the "new" revision
&$links: Array of HTML links
+$oldRev: Revision object of the "old" revision (may be null)
'DiffViewHeader': Called before diff display
$diff: DifferenceEngine object that's calling