Pathological

This update changes the way units detect their target. Since I can reliably tell whether your tank is trying to move toward another tank, vs moving into a city, this fixes a lot of bugs. Details for Code-Heads here.

I also made the AI moves follow a diagonal/zig-zag path. Previously the AI moved in an "L" shape. Technically this is correct and it doesn't matter. That said, moving all in straight lines looked silly to me, so I have changed it. The movement method also uses real path finding now, so once I have islands it should continue to work properly.