anchor.diff:  %%--------------------------------------------------------------------
   %% Function: behaviour_info(callbacks)
   %% Descrip.: Describe all the API functions a module indicating it is
  -%%           an sipuserdb behaviour module must export. List of tuples
  -%%           of the function name and it's arity.
  +%%           a sipuserdb behaviour module must export. List of tuples
  +%%           of the function names and their arity.
   %% Returns : list() of tuple()
   %%--------------------------------------------------------------------
   behaviour_info(callbacks) ->
  
positive.code:     logger:log(debug, "Userdb: ~p:get_users_for_addresses_of_record ~p -> ~p", [Src, Addresses, Res]),
      Res.
  
  % Gets all addresses for a user. Used for example
  % to check if a request from a user has an acceptable
  % From: header.
  get_addresses_for_user(User) ->
      {Src, Res} = module_apply(get_addresses_for_user, [User]),
      logger:log(debug, "Userdb: ~p:get_addresses_for_user ~p -> ~p", [Src, User, Res]),
  
negative.code:     {"*", nomatch};
  module_apply([Module | NextModule], Function, Args) ->
      case apply(Module, Function, Args) of
  	error ->
  	    logger:log(error, "Userdb: Error was returned from ~p:~p (arguments ~p), "
  		       "throwing '500 Server Internal Error'",
  		       [Module, Function, Args]),
  	    throw({siperror, 500, "Server Internal Error"});
  	nomatch ->
  	    module_apply(NextModule, Function, Args);
  