diff: don't crash when merged-in addition is copied Similar to what was explained in the previous commit, the diff code expected copy source to be in "ctx1", which is not always the case during a merge. This has been broken since before hg 2.0. Also similar to the previous commit, we fix the problem by fixing up the copy dict.

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.