Skip draw by repetition check in qsearch

Cut in half the time spent in pos.draw() that accounts
for a whopping 1% of total time !

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

src/position.h

@@ -228,7 +228,7 @@ public:
 
   // Game termination checks
   bool is_mate() const;
-  bool is_draw() const;
+  template<bool SkipRepetition> bool is_draw() const;
 
   // Number of plies from starting position
   int startpos_ply_counter() const;