0.8.2.33

0.8.2.33
	Implement INTERRUPT-THREAD, which forces another thread to
	execute a function supplied by the caller.

	In the process, design a mostly entirely new scheme for
	calling Lisp code as a result of a handled signal: instead of
	calling into Lisp directly, frob the signal context and the
	stack to arrange that the Lisp is called after the signal
	handler itself has returned.  This is expected to be
	applicable to signal handlers generally (and will have portability
	benefits), but needs them to be changed around to call it.
	Presently it's used only for interrupt-thread (SIGRTMIN)
	and control stack exhaustion (one branch of SIGSEGV)

	In principle, all you need do to use this in other places is
	call return_to_lisp_function in the signal handler, with the
	context and the function object that you wish to be called.
	For the x86 you also need to make sure the signal is being
	handled on the alternate signal stack, otherwise you'll
	overwrite your own stack frame.