Locks don't get released if exceptions occur within with blocks

[rwb27]

If something fails while it has acquired a lock using a with block, it appears the lock doesn't get released.

I think this needs a tweak to the StrictLock code.

[rwb27]

Correction: this only happens if the lock is acquired with arguments. That means

with mylock:
    raise Exception

does (correctly) release the lock, whereas

with mylock(timeout=None):
    raise Exception

does not.

I'll make a MR to fix this.