I never liked it, but with C2x coming out, it's best to handle bools
properly. I haven't gone through all the uses of int as bool (I'll leave
that for fixing when I encounter them), but this gets QF working with
both c2x (really, gnu2x because of raw strings).
I added Sys_RegisterShutdown years ago and never really did anything
with it: now any system that needs to be shutdown can ensure it gets
shutdown on program exit, and in the correct order (ie, reverse to init
order).
