manifest: add optional recording of clean entries to diff This makes manifest slightly easier to use for status code.

context: use manifest.diff() to compute most of status We can do a little tiny bit better by enhancing manifest.diff to optionally include files that are in both sides. This will be done in a followup patch.

trydiff: replace dodiff=True/'binary' by binarydiff=False/True

trydiff: replace 'dodiff = False' by 'continue' The 'dodiff' variable is initialized to True and may later be set to either False or "binary". When it's set to False, we skip everything after that point, so we can simplify by instead continue-ing (the loop). We can then also drop the 'if dodiff', since it will always be true.