RE: virtual timers and System.system

[Simon Marlow]

> The correct handling would be:
> - block SIGALRM/SIGVTALRM/SIGPROF
> - *then* fork() (else you have a race condition where the child could
>   receive *and handle* the signal)

This race condition is harmless, I think.  The VTALRM handler just
increments a counter, and we're about to blow away this process anyway.

Cheers,
        Simon