No Tempo for draw scores given by heuristic functions

The current master applies Eval::Tempo even to leaves evaluated
as draw by some of the static evaluation functions of endgame.cpp
(for instance KNN vs K or stalemates in KP vs K). This results in
some lines being reported as +0.07 or -0.07 when the terminal
position has reached such endgames (0.07 being about the value
of a tempo for Stockfish).

This patch does not apply Eval::tempo to these positions. This leads
to more nodes being evaluated as VALUE_DRAW during search, giving more
opportunities for cut-offs in alpha-beta.

STC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 52602 W: 11776 L: 11403 D: 29423
http://tests.stockfishchess.org/tests/view/5a8cb8f60ebc590297cc8546

LTC:
LLR: 2.97 (-2.94,2.94) [0.00,4.00]
Total: 156613 W: 26820 L: 26158 D: 103635
http://tests.stockfishchess.org/tests/view/5a8f452d0ebc590297cc865a

Bench: 4924749

src/evaluate.cpp

@@ -880,7 +880,8 @@ namespace {
         Trace::add(TOTAL, score);
     }
 
-    return pos.side_to_move() == WHITE ? v : -v; // Side to move point of view
+    return  (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
+           + Eval::Tempo;
   }
 
 } // namespace
@@ -890,7 +891,7 @@ namespace {
 /// evaluation of the position from the point of view of the side to move.
 
 Value Eval::evaluate(const Position& pos) {
-  return Evaluation<NO_TRACE>(pos).value() + Eval::Tempo;
+  return Evaluation<NO_TRACE>(pos).value();
 }
 
 
@@ -904,7 +905,7 @@ std::string Eval::trace(const Position& pos) {
 
   Eval::Contempt = SCORE_ZERO; // Reset any dynamic contempt
 
-  Value v = Evaluation<TRACE>(pos).value() + Eval::Tempo;
+  Value v = Evaluation<TRACE>(pos).value();
 
   v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view