* mutex_destroy() only checked wether or not there were waiters,
not if the lock itself was presently held by another thread.
Now we do, which should make #15015 panic much earlier instead
of trying to use freed memory.
* mutex_transfer_lock() and recursive_lock_transfer_lock() did
not check that the calling thread actually owned the lock.
Now it does, which should trigger asserts if anyone tries
to do this.
c2cbf95810