contification paper

[Stephen Weeks]

> I would be very very surprised if the getrusage() times go down, although I
> could imagine, due to race conditions, a problem if you compared a times()
> result to a later getruage() result, or vice versa.

This is actually done in the timeToString function in control.sml, which
subtracts the gc time (as computed by getrusage) from the total time (as
computed by times) to get the nongc time.

I'm beginning to think that the right fix is to use times in gc.c.