Fix race condition in alarm lock processing noticed by Richard Sharpe <realrichardsha...

Fix race condition in alarm lock processing noticed by Richard Sharpe <realrichardsharpe@gmail.com>.
"It seems to me that if the lock is already held by another process when we
enter this code, there is a race between the timeout and the granting. If
the lock is subsequently granted, the process releasing the lock will signal
the wait variable (or whatever) and our process will be scheduled. However,
if the timeout occurs before we are scheduled, the timeout will be delivered
first.

We will have the lock but will forget we have the lock, and never release
it."
Jeremy.