0.8.3.1

0.8.3.1

	Merge stop_the_world branch: a new scheme for stopping threads
	during GC, that avoids the use of ptrace and lets any of the
	threads stop any of the others.  This is a summary log entry:
	see branch commits for details

	New C functions maybe_defer_handler and run_deferred_handler,
	which encapsulate a lot of the "is it safe to run this handler
	now?  no, ok, copy its siginfo somewhere safe and do it later"
	cruft that's presently done ad hoc.

	Stack scavenging now looks for esp in the most recent
	interrupt context for each thread.  Requires that threads
	save said interrupt contexts in sig_stop_for_gc_handler

	Clean up some compiler warnings in gencgc.c

	Lisp-level changes: approximately a reversion to old-style (or
	single-threaded) GC.  Haven't actually added the gc hooks back
	in yet, but now there's at least a place for them to go.

	Lock around SUB-GC to remove window that may allow two threads
	to attempt to collect at once.

	WITHOUT-INTERRUPTS around SUB-GC to protect c-level spinlocks
	used in gc_{stop,start}_the_world

	(C-level spinlocks are just integers manipulated by get_spinlock(),
	release_spinlock().  There's no unwind-protect or anything
	involved in their use, so a thread interrupted when it's
	holding one of these will continue to hold it)

	Remove #if 0 from around the copying of sigmask in
        undo_fake_foreign_function_call.  Replace sizeof(sigmask_t)
        with an expression involving the value of NSIG and the rash
        assumption that sigset_t is a bitmask.

	Moved get_spinlock into foo-arch.h and made it static inline.
	Added release_spinlock for parity

	Delete irritating message from sigcont_handler

	New test cases