signal handling and save world

[Matthew Fluet]

> If you restore a world which was doing profiling when it was saved, do you
> really want to try to set profiling go again?  Not clear to me.

Well, I want it because I want to profile the compiler, not just
processing the basis library.

> Either way, you definitely want to do the sigaltstack().
> I don't see though how moving it from GC_init() to GC_initCounters() will
> change anything.  Isn't the latter only called from the former?

GC_initCounters is called both from GC_init and GC_loadworld.  I agree
that it doesn't quite belong there, but it was the quick place to put it.

> Any way, I put a tar'd gzip'd version of the profiling bug stuff at
> 	http://sourcelight.com/Z/profBug.tgz

thanks.