Module pidfile

Confirm that the given lockfile contains our pid. Should be entirely unecessary, but paranoia always served me well.

Tries to write a lockfile containing the current pid. Excepts if the lockfile already contains the pid of a running process.

Although this should prevent a lock from being granted twice, it can theoretically deny a lock unjustly in the unlikely event that the original process is gone but another unrelated process has been assigned the same pid by the OS.