tests: add test showing that rebase of extinct commit with successor fails As the test case shows, attempting to rebase a commit that has a successor that is not in the rebase set and not in the destination currently fails because it "will cause divergences". However, it doesn't seem like there's any harm in skipping the extinct commit. I suspect this case missed simply because extinct revisions are usually hidden. Differential Revision: https://phab.mercurial-scm.org/D4407

tests: add log output after stripping for context for next test It's not obvious what the repo state will be after stripping some nodes and obsmarkers, so let's include the log output to make it easier to follow the test case that comes after. Differential Revision: https://phab.mercurial-scm.org/D4406

obsutil: make sure "addedmarkers" is not None in getobsoleted() Similar reasoning as in 52e6171ec822 (obsutil: make sure "addedrevs" is not None in getobsoleted(), 2018-08-25). Differential Revision: https://phab.mercurial-scm.org/D4411