Some changes to Benchmark.hs.
Change firing strategy of CleverAI for movable ships.

For an explanation, see the comment in the source code.
Finally fixed that bug... (in game control)

When determining which ship was fired at, don't consider the sunk ones because they are "gone".
The problem was this: Ship A is sunk. Ship B moves on top of ship A. If you fire at A, you
sometimes get the result for B (namely "Sunk") instead of the result for A (namely "Hit").
This confused the AI very much.
Merge branch 'master' of https://github.com/zrho/afp