Properly deal with draw by repetition

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When 2 chess engines battle against each other, they might enter a board
configuration where they continue to repeat moves in a circular manner,
thus the board never advancing.
These cases can spawn for more than 2 board states, for example: A->B->C->A
(3 board states)

These cases need to be properly analyzed and dealt with. Either by making a
move that exists the cycle or by offering a draw by repetition.

Original issue reported on code.google.com by Valentin Stanciu on 21 Jun 2009 at 11:22