fixed problem with GLUT and new versions of MACOS

Author: miccol

src/behavior_tree.cpp

@@ -19,7 +19,7 @@ void Execute(BT::ControlNode* root, int TickPeriod_milliseconds)
 {
     std::cout << "Start Drawing!" << std::endl;
     // Starts in another thread the drawing of the BT
-    //std::thread t(&drawTree, root);
+    std::thread t(&drawTree, root);
 
     root->ResetColorState();