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/ShapeDrawable

@@ -177,14 +177,14 @@ class OSG_EXPORT ShapeDrawable : public Drawable
         /** Accept a PrimitiveFunctor and call its methods to tell it about the internal primitives that this Drawable has.*/
         virtual void accept(PrimitiveFunctor& pf) const;
 
+        virtual BoundingBox computeBound() const;
+
     protected:
 
         ShapeDrawable& operator = (const ShapeDrawable&) { return *this;}
 
         virtual ~ShapeDrawable();
 
-        virtual bool computeBound() const;
-
         Vec4 _color;
 
         ref_ptr<TessellationHints> _tessellationHints;