Fixed an old pathfinding issue

The enemy AI checks all the places it can go to in order to work out the best one. This lead to some nice complex behaviour with a relatively simple system. Because they don't have a specific goal in mind it didn't make much sense to use pathfinding algorithms for them. But then I had some situations where checking more than one turn in advance was required due to blocked hexes. I've implemented a little system where it checks a few turns ahead for certain things and it seems to be working.

Here you can see the enemy ship avoids my rather obvious trap!