Merge Gary's bishop_pin patch

Give a bonus if a bishop can pin a piece or can
give a discovered check through an x-ray attack.

Seems good after 24000 games at 15"+0.05 (single thread):

ELO: 12.30 +- 99%: 5.79 95%: 4.40 LOS: 100.00%
Total: 24000 W: 4931 L: 4082 D: 14987

bench: 4917064

diff --cc src/evaluate.cpp
index 5140c4932ab022ab53b94268188363b4404eba4b,02810b78490093f1f14f7c220897f2661f4bc63f..3ba405ccf28ff378192bed7b905ef1fc9f9686c9
--- 1/src/evaluate.cpp
--- 2/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@@ -593,7 -583,12 +583,14 @@@ Value do_evaluate(const Position& pos, 
          // of threat evaluation must be done later when we have full attack info.
          if (ei.attackedBy[Them][PAWN] & s)
              score -= ThreatenedByPawnPenalty[Piece];
 -        else if (Piece == BISHOP && (PseudoAttacks[Piece][pos.king_square(Them)] & s)) {
 -             const Bitboard between = BetweenBB[s][pos.king_square(Them)] & pos.pieces();
 -             if (!more_than_one(between))
 +
++        // Otherwise give a bonus if we are a bishop and can pin a piece or
++        // can give a discovered check through an x-ray attack.
++        else if (    Piece == BISHOP
++                 && (PseudoAttacks[Piece][pos.king_square(Them)] & s)
++                 && !more_than_one(BetweenBB[s][pos.king_square(Them)] & pos.pieces()))
+                  score += BishopPinBonus;
 -        }
+ 
          // Bishop and knight outposts squares
          if (    (Piece == BISHOP || Piece == KNIGHT)
              && !(pos.pieces(Them, PAWN) & attack_span_mask(Us, s)))