I've now committed all of this. I ended up finding a couple other frontend
programs that called pqsignal() with an invalid signal number on Windows,
so I fixed those as well. AFAICT the reason I didn't catch them in my
earlier testing is because they aren't tested! I'll keep an eye on the
buildfarm for any problems with the SIG_* redefinition removal, too.
Thanks for reviewing and for sharing lots of context about this stuff.
--
nathan
