anchor.diff:  handle_call(nodes_actual_proper, _From, State) ->
       {reply, do_nodes_actual_proper(), State};
   
  -handle_call(nodes_wanted, _From, State) ->
  -    {reply, do_nodes_wanted(), State};
  -
   handle_call(Msg, _From, State) ->
       ?log_warning("Unhandled ~p call: ~p", [?MODULE, Msg]),
       {reply, error, State}.
  
positive.code: % Read from ns_config nodes_wanted.
  
  do_nodes_wanted() ->
      case ns_config:search(ns_config:get(), nodes_wanted) of
          {value, L} -> lists:usort(L);
          false      -> []
      end.
  
negative.code:     lists:subtract(nodes_actual_proper(), [node()]).
  
  nodes_wanted() ->
      do_nodes_wanted().
  
  % API's used as callbacks that are invoked when ns_config
  % keys have changed.
  