run-tests: allow bisecting a different repo
Add `--bisect-repo` flag which accepts a different repo to bisect.
3rd party extensions may reuse `run-tests.py` from core to run tests. Test
failure could be caused by either a core hg change or the 3rd party
extension code itself. Having a way to specify which repo to bisect is
useful.
Differential Revision: https://phab.mercurial-scm.org/D578
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).