0.8.4.1

0.8.4.1
	Merge most of atropos-branch: miscellaneous (mostly threading)
	fixes that were probably a little too risky for late in 0.8.4
	development.

        doc/ - fix up some of the sgml errors that sourceforge keeps
        mailing me about

        New function release-spinlock that only changes the lock value
        if we owned the spinlock, so good for unwind-protect cleanups
        when lock acquisition failed

        get-spinlock release-spinlock current-thread-id could all win
        from being inlinable

        Use a RT signal (SIG_DEQUEUE) for resuming threads that were
        on queues, instead of having SIGCONT do both this and the
        resume-after-gc task.

        Scattered commentary describing the state of the signal mask
        in various interesting places

        In gencgc alloc, only install a deferred handler for GC if
        there was no previous handler for anything else.  This fixes
        a longstanding bug where the GC thread would eat all cpu while
        waiting indefinitely for othr threads to stop.

        Add SIG_STOP_FOR_GC to the blockable list

        interrupt_maybe_gc_int: enable signals before calling SUB-GC,
        or the locking that sub-gc does is going to interact badly.

        Minor rearrangement to parent thread to stop it having to wake
        up on every GC

        Add grovel_headers line for SIG-DEQUEUE.  OAOOM alert...