Make damage() use roundavg()

Make damage() use roundavg()

Turns damage() into a one-liner.

damage() now uses random() % 32768 in chance() instead of random() %
100 inline, therefore can round differently for the same pseudo-random
number.  Update expected smoke test results accordingly.

Aside: "random() % n" distributes evenly only when n is a power of
two.  100 isn't.  However, because random() yields at least 31 bits,
and 100 is so much smaller than 2^31, the error is vanishingly small.