compat: adapt to change in mercurial core The code around merge destination have been changed in core, we do some basic adaptation to make sure we don't crash. Further rework to adapt//take advantage of core change would probably be useful but this is not the point of this commit.

topic: handle merge.update function signature change I think this is backwards compatible with how it used to be called, but I didn't worry about it too much either.

Merge.

test-topic-dest: test fixes I should have put in the previous change I split a bigger change from marmoute that included some rebase support that I wanted to discuss more, but I didn't correctly commit my fixes to the tests before pushing. Oops.

topic: fix changing topics of commits that have an amend_source Includes a test for this specific case, but we should probably spend more time squinting at the interactions between the current topic wrapper function and commitctx for memctx instances.

topic: remove useless call to c.parents()