Bugfix on new castling method

Bugfix on new castling method

Copying the Rook square in stead of growing a Rook was done after the
Rook square had already been cleared. In addition the Rook ended up on
d1 for e1b1 castling. To fix that, the alternated step vector had to be
calculated in advance, before being sure it would be applied, to be
available in the castling code. The variable v is now used as a
temporary for that, as it was available after the score is minimaxed.