*********************** 05/26/2000 20:31 **********************************
* Changed listnode attr TYPELIST/VARDLIST to represent [type/vardecl]_listoflist instead
of [type/vardecl]_list struct. Updated "\4add_var_type_layer" special fn. Updated op_to_function()
that used it. 
* Removed unused meta interp code from validate_function() - now done in interpret_meta_code()
* Added NULL pointer verification in "\4add_var_type_layer" and get_type_by_name()
