Disable templetized operators by default

To avoid nasty bugs due to silently overriding of
common operator we enable the templates on a type
by type base using partial template specialization.

No functional change, zero overhead at runtime.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/piece.h

@@ -43,6 +43,9 @@ enum Piece {
   BP = 9, BN = 10, BB = 11, BR = 12, BQ = 13, BK = 14, PIECE_NONE = 16
 };
 
+ENABLE_OPERATORS_ON(PieceType);
+ENABLE_OPERATORS_ON(Piece);
+
 
 ////
 //// Constants