Made Refernced::setThreadSafeReferenceCounting(bool) a virtual then overrode

this in various scene graph classes to ensure that the scene graph gets
updated as well as the objects that the initialial call is made from.

src/osgViewer/View.cpp

@@ -22,7 +22,11 @@ using namespace osgViewer;
 View::View()
 {
     // osg::notify(osg::NOTICE)<<"Constructing osgViewer::View"<<std::endl;
-   setEventQueue(new osgGA::EventQueue);
+
+    // make sure View is safe to reference multi-threaded.
+    setThreadSafeRefUnref(true);
+
+    setEventQueue(new osgGA::EventQueue);
 }
 
 View::~View()