Allow SearchStack to link an EvalInfo object

This will allow to have wider access to attack
information, for instance from MovePicker.

Note that 'eval' field become obsolete, it is kept
just becasue when we get a position score from TT
we update 'eval' even without an EvalInfo object.

No functional change.

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

src/search.cpp

@@ -653,6 +653,7 @@ void SearchStack::init(int ply) {
   currentMove = threatMove = MOVE_NONE;
   reduction = Depth(0);
   eval = VALUE_NONE;
+  evalInfo = NULL;
 }
 
 void SearchStack::initKillers() {
@@ -1375,14 +1376,15 @@ namespace {
     const int FutilityValueMargin = 112 * bitScanReverse32(int(depth) * int(depth) / 2);
 
     // Evaluate the position statically
-    if (isCheck)
-        ss[ply].eval = VALUE_NONE;
-    else
+    if (!isCheck)
     {
         if (tte && (tte->type() & VALUE_TYPE_EVAL))
             staticValue = value_from_tt(tte->value(), ply);
         else
+        {
             staticValue = evaluate(pos, ei, threadID);
+            ss[ply].evalInfo = &ei;
+        }
 
         ss[ply].eval = staticValue;
         futilityValue = staticValue + FutilityValueMargin;