deadlock handler

There is a certain level of deadlock detection/avoidance built into the record locking facility. This deadlock handling provides the same level of protection granted by the /usr/group standard lockf call. This deadlock detection is only valid for processes that are locking files or records on a single system. Deadlocks can only potentially occur when the system is about to put a record locking system call to sleep. A search is made for constraint loops of processes that would cause the system call to sleep indefinitely. If such a situation is found, the locking system call will fail and set errno to the deadlock error number. If a process wishes to avoid the use of the system's deadlock detection, it should set its locks using F_SETLK instead of F_SETLKW.