Fix posting submitted changelists for perforce.
Review Request #5837 — Created May 16, 2014 and submitted — Latest diff uploaded
The code to post submitted changelists would end up posting a diff for both
the intended change and the one preceeding it. This is because we passed in
our (base, tip] revisions for 'p4 filelog', which itself behaves as [base,
tip]. To work around this, I've added code to increment the base revision
before calling filelog.
Ran unit tests.