Refactored the UserDataContainer so that the osg::UserDataContainer is now a pure virtual base class,

with a osg::DefaultUserDataContainer subclassed from this.  The user object access methods have now all
been moved from osg::Object into the UserDataContainer class, except for the set/getUserData() methods
that are left in osg::Object for backwards compatibility, and the description list access methods have
been moved back into osg::Node.

main UserObject access methods are now all def

src/osgWrappers/serializers/osg/Object.cpp

@@ -1,4 +1,5 @@
 #include <osg/Object>
+#include <osg/UserDataContainer>
 #include <osgDB/ObjectWrapper>
 #include <osgDB/InputStream>
 #include <osgDB/OutputStream>
@@ -45,6 +46,6 @@ REGISTER_OBJECT_WRAPPER( Object,
     UPDATE_TO_VERSION( 77 )
     {
         REMOVE_SERIALIZER( UserData );
-        ADD_OBJECT_SERIALIZER( UserDataContainer, osg::Object, NULL );
+        ADD_OBJECT_SERIALIZER( UserDataContainer, osg::UserDataContainer, NULL );
     }
 }