Prevent player from making winning move between A1 and C1

[ericmathison]

Currently, the computer will not reliably or "intentionally" prevent the player from making a winning move between A1 and C1.

For example, given a player X and computer O:

   1 2 3
A  X - -
B  - - O
C  X - -

The computer will not consistently move to B1.

Adding a condition for this will fix the immediate bug but we should be using systematic checks for two in a column/row/diagonal with a blank space. Also since tic tac toe has such a small combination of possible moves, we should have a comprehensive test suite.

[ericmathison]

Fixed by 77a29f9