run-tests: error out on `--local --with-[c]hg` I don't see much reason to allow these combinations. You could use --local and override only one of --with-hg or --with-chg, but I don't see much practical use for that. It would be easy to work around anyway by passing both --with-hg and --with-chg. By erroring out, it makes the code a bit easier to reason about to allow the next few patches. Differential Revision: https://phab.mercurial-scm.org/D6759