Added a AnimationPathCallback which can update both a MatrixTransform and a

PositionAttitudeTransform, removed the equivialnt callbacks once found in these
transform classes.

Changed the NodeCallback class so its derived from osg::Object instead of
osg::Referenced to allow it to be saved out in the .osg format.

Added support for Update and Cull callbacks into the .osg file format.

Added support for AnimationPathCallback into the .osg file format.

src/Demos/osgpbuffer/osgpbuffer.cpp

@@ -248,7 +248,7 @@ class MyGeometryCallback :
                 osg::Vec3* end = begin+count;
                 for (osg::Vec3* itr=begin;itr<end;++itr)
                 {
-                    osg::Vec3 dv(*itr-_origin);
+                    osg::Vepc3 dv(*itr-_origin);
                     osg::Vec3 local(dv*_xAxis,dv*_yAxis,dv*_zAxis);
                     
                     local.z() = local.x()*_amplitude*