About to check in a big signal handling patch

[Christopher Faylor]

I'm about to check in YA rewrite of the signal handling code.  This
implements some of the logic needed to handle signals-to-threads and
(ta da) sigwait.

The code isn't perfect yet and still requires some tweaking.  I'm not
entirely wild about certain implementation details -- alternatives are
still occuring to me at 2AM as I'm drifting off to sleep, on my thinking
pedestal, and in the shower.  I just need to get this checked in so that
I can start getting some revision control.

When I'm done, I will have siginfo stuff working as well as some
rudimentary timer_* and clock_* implementations.

So, no bug reports on it yet.  I'll let you know when I think it is
perfect.  :-)

cgf