Fixed infinite loop in combat

Combat results were done with a formula of
X = X - A/n-1 - B/n-1...

The computation of A/n-1 needs to round up so that small numbers still
remove at least 1 ship. Else a battle between 3 ships from 3 players
would never end. They would be subtracting 1/2 ships (rounded down) and
never get down to 1 fleet.