Fixed bug which was causing the chess board model to contain duplicate
references to the same piece, creating the side effect of causing some
legal moves to be recognized as non-legal move. Ultimatly the bug was
caused by a copy and paste error, where when passing paramaters from
playerHasLegalMove to kingInCheckAfterMove the same paramater was passed
as both the piece moved and the piece captured. This created an
additional reference so that there was no null reference to use when
un-doing the move, creating extra references on the board.