hg: allow hg.parseurl(url, None) In many places hg.parseurl is called with a url and "opts.get('rev')", suggesting the second, optional argument can be None. Because opts['rev'] usually defaults to [] this never happens in practice. However, extensions don't necessarily behave the same, but do copy this pattern. Also, include wider hg.parseurl tests, beyond a demonstration of the problem.

transplant: remove the restriction that the destination be nonempty. Test fixed by Patrick Mezard <pmezard@gmail.com>