Switch over to using a real hg repo instead of a bundle.

The 'hg' command-line tool doesn't entirely work when treating a .bundle file
as if it were a repo. This change extracts the bundle into a new hg repo
directory, and changes our test suite over to use it.

Testing done: Ran unit tests.
Add latest Diff timestamp. Review last activity does not represent diff activity.

Review last activity does not represent diff activity. One can not see if the
newer diff has been uploaded or just comment added. This change adds another
timestamp to the header of the review request box to show when the last version
of the diff was added.

Testing Done:
Tested manually on my development RB install.

Reviewed at https://reviews.reviewboard.org/r/4898/
Fix some format strings for localization.

Some format strings for SCMErrors were formatting multiple values without using
named formatters, which makes it impossible for translators to reorder the
sentence.

Testing done:
* Ran unit tests
* Extracted message catalogs and didn't see any errors.

Reviewed at https://reviews.reviewboard.org/r/5068/
Rename "Add Comment" to "New Comment"

Short of a redesign of the comment dialog to clear up the issues with replying
to existing comments vs. creating new ones, renaming this may help with some of
the confusion.

Suggested at bug 3160.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	reviewboard/templates/reviews/review_request_box.html