+/** Walks over all classes information reachable from global roots.
+ Touches every class in specified order:
+ - first the super class
+ - second the class itself
+ - third the sub classes. If new classes are created
+ during the traversal these will be visited, too. **/
+/** @@@ shoulc be named class-walk **/
+void type_walk_super2sub(void (pre)(type_or_ent*, void*),
+ void (post)(type_or_ent*, void*),
+ void *env);