Use revision parsing for perforce diffs, refactor pending change posting.
This change uses parse_revision_spec inside the perforce diff routine, and does

some refactoring to clean up the method for posting pending changes. There was

some code in here that theoretically would handle non-pending changes, but

since 'p4 opened' doesn't work for submitted changes, that was effectively dead

code. I'll be handling that later once I implement two-revision diffs.
The one unexpected change in the diff hashes is when we're dealing with moved

files when the server doesn't have the capability. The reason for the hash

change is that the new list of repo files in the test case is iterating in a

different order than the dict.

Posted changes for pending changesets that involved added, moved, and deleted

  files.
Ran unit tests