Unify 'ponderhit' handling

Finally we can now merge the 'ponderhit' case with
'stop' and 'quit'.

The patches have been done step by step to help debugging
becuase this is really tricky code.

No functional change.

src/uci.cpp

@@ -66,19 +66,14 @@ void UCI::loop(const string& args) {
 
       is >> skipws >> token;
 
-      if (token == "quit" || token == "stop")
+      if (token == "quit" || token == "stop" || token == "ponderhit")
       {
-          Search::Signals.stop = true;
-          Threads.main_thread()->wake_up(); // Could be sleeping
-      }
-      else if (token == "ponderhit")
-      {
-          // GUI sends "ponderhit" if we were told to ponder on the same move the
+          // GUI sends 'ponderhit' to tell us to ponder on the same move the
           // opponent has played. In case Signals.stopOnPonderhit is set we are
-          // waiting for "ponderhit" to stop the search (for instance because we
+          // waiting for 'ponderhit' to stop the search (for instance because we
           // already ran out of time), otherwise we should continue searching but
           // switching from pondering to normal search.
-          if (Search::Signals.stopOnPonderhit)
+          if (token != "ponderhit" || Search::Signals.stopOnPonderhit)
           {
               Search::Signals.stop = true;
               Threads.main_thread()->wake_up(); // Could be sleeping