Re: SIGQUIT handling, redux

I wrote:
> I'll take a closer look at the idea of using _exit(1) tomorrow,
> but I'd be pretty hesitant to back-patch that.

Here's a patch for that; it passes light testing, including forcing
the backend through the SIGTERM and timeout code paths. There's
not much to it except for changing the signal handlers, but I did
add a cross-check that no on-exit handlers have been registered
before we get done with using these signal handlers.

I looked briefly at the idea of postponing ProcessStartupPacket
until InitPostgres has set up a fairly normal environment. It
seems like it'd take a fair amount of refactoring. I really
doubt it's worth the effort, even though the result would be
arguably cleaner logic than what we have now.

regards, tom lane