diff: don't crash when merged-in addition was removed (issue4786) During a merge, if the user removes a file that came from parent 2 and did not exist in parent 1, the file's status will be "removed". This surprises the diff code, which crashes because it expects removed files exist in parent 1. This has been broken since 377124ba6b10 (trydiff: use 'not in addedset' for symmetry with 'not in removedset', 2014-12-23). Fix by fixing up the list of removed file, similar to how we currently fix up the list of modified and added files during a merge.