Implement new interprocess lock

[Squadrick]

Complete rewrite of the reader writer lock using pthread directly, and check for EOWNERDEAD to prevent resource starvation

[Squadrick]

IPC_Lock::consistency_handler()'s handling of the ENOTRECOVERABLE error code from pthread_mutex_lock() does not look right. The process that gets this error code does not acquire the lock, yet unlock is called later. Also destroying and reinitializing an object without holding any locks seems really racey. I don't know if there is a sensible way of recovering from this error.

[Squadrick]

There are more problems when a process dies that is holding a lock. counter never gets updated. Also, a writer could acquire the g lock even if there are many readers if the one reader that is actually holding the lock dies, then the writer would think it would have unique ownership when there are actually many readers out there. Also is a pthread_mutex allowed to be unlocked by a different thread/process than what locked it? From a quick glance of the docs it seems like not, but I didn't look hard.