0.8.13.65

0.8.13.65
	Fix/bandaid for some more threading problems (though
	regrettably only the easy ones)

	... when stopping threads for GC, if kill() fails assume this
	    is because the thread died after outliving its parent so
	    nothing was available to set th->state=STATE_DEAD when it
	    exited.  Mark said thread dead, Ted.

	    (Note: still doesn't cope with pid recycling.  In the
	    unlikely-unless-malefactor-involved case that a pid
	    previously used for a thread died after its parent and now
	    belongs to an unrelated process which the current user has
	    permission to kill it, it will probably die in the next
	    GC.  Exploits on a postcasrd to the usual address, please)

	... interrupt_thread() now checks that the thread is one we
	    know about (instead of just some random other process)
	    and refuses to kill if it's not.  INTERRUPT-THREAD now
	    catches this and other errors from kill() and signals a
	    more useful condition than the provious "unexpected system
	    call failure"

        ... only the parent of a thread can identify whether it is a
            zombie, which it should usually do when it gets a
            SIG_THREAD_EXIT.  It's possible that this signal may go
            missing if delivered during pseudoatomic or similar, so
            for the sake of being able to GC we ask each thread to
            check its children again in the stop_for_gc_handler before
            going to sleep

	Thread documentation update based on the LSM lightning talk