Refactored the way the Scene is used in Viewer and CompositeViewer to ensure

that only on Scene exists per scene graph.

include/osg/GraphicsThread

@@ -15,6 +15,7 @@
 #define OSG_GRAPHICSTHREAD 1
 
 #include <osg/OperationThread>
+#include <osg/State>
 
 namespace osg {
 
@@ -117,6 +118,19 @@ public:
     
 };
 
+class OSG_EXPORT EndOfDynamicDrawBlock : public OpenThreads::BlockCount, public osg::State::DynamicObjectRenderingCompletedCallback
+{
+    public:
+    
+        EndOfDynamicDrawBlock(unsigned int);
+    
+        void completed(osg::State* state);
+
+    protected:
+
+        ~EndOfDynamicDrawBlock() {}
+};
+
 }
 
 #endif