program dying due to stack overflow doesn't call signal handlers

[dankamongmen]

I had a bug in ncman which resulted in an infinite recursion. Upon receiving its SIGSEGV, the terminal was not restored to its original mode. The SIGSEGV handler never appeared to be called. I think establishing an alternate signal handler stack early on will work around this problem; we should probably do so.

[dankamongmen]

Hrmmm, I'm not sure sigaltstack() is process-wide; it might just be for the calling thread =.

[dankamongmen]

yeah, it's per-thread, urk. well, we can't control everyone else's threads, but we can handle our own, i suppose.

[dankamongmen]

done, tested, works