0.8.4.8

0.8.4.8
	More thread fixes: now passes the cl-ppcre thread test

	... all_threads_lock needed to be declared volatile

	... new 'state' field in struct thread, to avoid race where
	the head of the all_threads list is reaped during stop_for_gc

	Removed "waitpid : child %d %x exited \n" message (rather,
	conditionalised it on show_thread_exit, which is default 0

	Remove unexplained (setsigmask 0) call in the repl, replaced
	with a call to warn_when_signals_masked so we can find out
	what it was for anyway.

	Default repl calls (get-foreground) - this is a unithread nop