Fixed a bug in ai_play(): index3 was being assigned incorrect values causing the omission of many possible moves by the computer. I also discovered having ai_play() try to win and prevent the opponent from doing the same was not simple. The function now only tries to prevent the opponent from winning. Also, it now only looks 2 moves into the future, looking too far ahead was causing it to fail in its goal.

The computer player should now be harder to beat than it was in version 1. The user interface was modified to prevent players from forgetting weather they are playing with an 'x' or an 'o'.