parents: avoid locking the repository during 'hg parents' The wrapping code was initially written for update and pull who need the lock anyway. We duplicated the logic in the parent case to remove the need for locking.

README: update instructions for running tests.

tests: remove the custom run-tests.py This test-runners is a copy from the Mercurial one and slowly drift out of sync. Use the Mercurial's core test runners instead.