Try to cleanup movepick

Hopefully without regressions.

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

src/movepick.h

@@ -2,17 +2,17 @@
   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
   Copyright (C) 2008 Marco Costalba
- 
+
   Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.
-   
+
   Stockfish is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
-  
+
   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
@@ -60,8 +60,7 @@ public:
     PH_STOP
   };
 
-  MovePicker(Position &p, bool pvnode, Move ttm, Move mk, Move k1, Move k2,
-             Depth dpth);
+  MovePicker(const Position& p, bool pvnode, Move ttm, Move mk, Move k1, Move k2, Depth d);
   Move get_next_move();
   Move get_next_move(Lock &lock);
   int number_of_moves() const;
@@ -77,8 +76,9 @@ private:
   void score_evasions();
   void score_qcaptures();
   Move pick_move_from_list();
-  
-  Position *pos;
+  int find_best_index();
+
+  const Position& pos;
   Move ttMove, mateKiller, killer1, killer2;
   Bitboard pinned, dc;
   MoveStack moves[256], badCaptures[64];