Fix interdiffs for deleted in a revision then modified in the future.
Review Request #7874 — Created Jan. 15, 2016 and discarded — Latest diff uploaded
A filediff for an interdiff would always display as deleted if it had been deleted in the first revision, even if the future revision no longer deleted the file. We now take the future filediff into account when calculating the deleted status.
./reviewboard/manage.py test -- reviewboard.diffviewer.tests