Make the "Diff Revision" label dynamically rendered in javascript.
In order to be able to update the displayed revision, this content needs to be

generated on the client side instead of the server.

Viewed various revisions of a diff, including interdiffs. Saw the expected

  text each time.
Checked that the "latest diff" and "See what's changed" links worked

  correctly.
Ran js-tests.
Ran jshint.