Rewrite bytes/sec calculation using fixed point math.

Rewrite bytes/sec calculation using fixed point math.

This makes signal handler safe on OpenBSD.

To avoid overflows the accuracy is scaled. Above 10 minutes run time
we only care about second accuracy. Between 1 seconds and 10 minutes
we use millisecond accuracy.

Below one second we use nanoseconds, but those numbers are probably
meaningless.

Signal handler problem pointed out by deraadt

OK deraadt, millert, tb