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
