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.

include/osg/Node

@@ -299,6 +299,9 @@ class OSG_EXPORT Node : public Object
         /** Get the const compute bound callback.*/
         const ComputeBoundingSphereCallback* getComputeBoundingSphereCallback() const { return _computeBoundCallback.get(); }
 
+        /** Set whether to use a mutex to ensure ref() and unref() are thread safe.*/
+        virtual void setThreadSafeRefUnref(bool threadSafe);
+
         /** Resize any per context GLObject buffers to specified size. */
         virtual void resizeGLObjectBuffers(unsigned int /*maxSize*/);