changelog: summarize the last couple of features

obshistory: create _fatemarkers() similar to _originmarkers()

obslog: makes --origin flag the default Test change have been carefully validated.

obslog: add a --origin flag to show predecessors instead of successors This flag will be turned on by default in the next changeset.

obslog: add preliminary support for showing predecessors This functionality is not yet used right now, but will be in the next patch.

obshistory: add _originmarkers() function to be used for obslog --origin

evolve: rename `evolve_source_*` to `divergence_source_*` This makes it clearer that this comes from divergence resolution.

evolve: mark new hash-salting extras keys as uninteresting for effect flag The user doesn't care if the `evolve_source_local`/`evolve_source_other` values in the extras changed, so this patch adds them to the blacklist that already exists for that purpose. This should also fix the flakiness we've seen in some tests. The flakiness seemed to stem from `mercurial.obsutil.geteffectflag()` not sorting extras keys. That means we ran into it relatively often for the `evolve_source_local`/`evolve_source_other` keys because there were two of them. That sorting bug should be fixed upstream.

evolve: handle relocation during divergence resolution producing no changes When resolving divergence and the two divergent commits have different parents, we start by rebasing one of them to have the same parent as the other. That step can result in no changes to commit. When it does, we would crash with a TypeError before this patch. This patch fixes it by instead creating an empty commit in that scenario. The existing code then continues to attempt to merge it, which produces no changes, and no commit is created on top. The other side of the divergence is marked as successor as usual, so orphans from the side that became empty will be evolved to the right place (see test).

tests: show crash from divergence resolution resulting in empty commit When relocating a commit results in an empty commit (because the changes are already in the destination), we get a TypeError from evolve.