-This is a lockfile implementation I created for use with cronjobs on
-my machine to prevent multiple copies of a job from running in
-parallel. When one job is running this code keeps a file on disk to
-indicate a lock is held. Other copies will fail to start if they
-detect this lock until the lock is released. There are provisions in
-the code for timing out locks, cleaning up a lock when a signal is
-received, gracefully retrying lock acquisition on failure, etc...
-