Shortcut see_sign() when SEE is known negative

This patch cuts 30% of SEE calculations, as a drawback
a returned negative value is no more always correct if
a shortcut is found.

This could impact move order when based on negative see
score as example bad captures and evasions.

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

src/position.h

@@ -229,7 +229,7 @@ public:
   void undo_null_move();
 
   // Static exchange evaluation
-  int see(Square from, Square to) const;
+  int see(Square from, Square to, bool shortcut) const;
   int see(Move m) const;
   int see(Square to) const;
   int see_sign(Move m) const;