Applied a patch from the wdoor-stable branch: Improved the logic avoiding human-human...

Applied a patch from the wdoor-stable branch: Improved the logic avoiding human-human match.

> commit 81d6582813f9af7f2c23c0f056ee6960b3299e05
> Author: Daigo Moriwaki <beatles@users.sourceforge.jp>
> Date:   Fri Dec 28 15:23:45 2012 +0900
>
>     - shogi_server/pairing.rb:
>       + There was a bug in the logic avoiding human-human match.
>         This issue has been fixed.
>       + Improved the logic avoiding human-human match. Human-human
>         matches will less likely happen.