Merge from vendor branch mlg:

Merge from vendor branch mlg:
Import unproven-pthreads, the mit-pthreads based cleanup I'm hacking on.

Why am I using MIT-Pthreads?  Because all the alternatives seem to have
very low level problems.  PTL2 has a locking problem of some sort that I
cannot track down, and the author insists that

	lock = PTHREAD_MUTEX_INIT;

is always to be legal, so he uses a pointer for locks.  This means
pthread_lock() can break in out of memory situations, and therefore so
can pthread_once(), and if you're using that to protect logging, and you
need to report a memory depletion, you're screwed.

--Michael