Added new Node/Drawable::s/getInitialBound and Node/Drawable::s/getComputeBoundCallback

methods and reimplement computeBound so that it passes back a bounding volume rather
than modifying the local one.

include/osg/ProxyNode

@@ -76,12 +76,12 @@ class OSG_EXPORT ProxyNode : public Group
         /** Get the object-space radius of the volume enclosed by the ProxyNode.*/
         inline float getRadius() const { return _radius; }
 
+        virtual BoundingSphere computeBound() const;
+
     protected :
     
         virtual ~ProxyNode() {}
 
-        virtual bool computeBound() const;
-
         void expandFileNameListTo(unsigned int pos);
 
         FileNameList        _filenameList;