Reformat trace code

Apart from usual renaiming, take advantage of
C++11 function template default parmeter to
get rid of Eval trampoline functions.

Some triviality fixes while there.

No functional change.

src/evaluate.h

@@ -31,9 +31,10 @@ namespace Eval {
 const Value Tempo = Value(17); // Must be visible to search
 
 void init();
-Value evaluate(const Position& pos);
 std::string trace(const Position& pos);
 
+template<bool DoTrace = false>
+Value evaluate(const Position& pos);
 }
 
 #endif // #ifndef EVALUATE_H_INCLUDED