jhp/tictactoe — pull request #1 by epriestley (2013-10-30 02:43:42+00:00)
Title: Fix an issue in detection of the squares for the left diagonal

Summary: There's an off-by-one error here which incorrectly detects these
positions as the left diagonal:

```
| |
-+-+-
X| |X
-+-+-
|X|
```

Adjust the calculation so the left diagonal is checked correctly.