lock: recognize parent locks while acquiring This is part of a series that will allow locks to be inherited by subprocesses in limited circumstances. This patch enables the logic introduced in previous patches.

test-lock.py: fix testing for forks The earlier test worked only because the held count went up to 2, so the first release brought it down to 1. Making a copy of the lock fixes that issue.

test-lock.py: allow PID to be changed in test state This will be used in upcoming patches to create locks that appear as if they're being created by child processes.

test-lock.py: add a lock wrapper that allows faking the PID This will be used in upcoming patches to create locks that appear as if they're being created by child processes.