Always use occupant JID as 'from' for room subject

When sending the room subject to a new participant, always use the
occupant JID that corresponds to the subject author as the 'from'
address.  It was already done this way when the subject was sent as part
of the room history.

src/mod_muc_room.erl

@@ -2475,14 +2475,15 @@ send_history(JID, Shift, StateData) ->
 			      lqueue_to_list(StateData#state.history))).
 
 send_subject(_JID, #state{subject_author = <<"">>}) -> ok;
-send_subject(JID, StateData) ->
+send_subject(JID, #state{subject_author = Nick} = StateData) ->
     Subject = StateData#state.subject,
     Packet = #xmlel{name = <<"message">>,
 		    attrs = [{<<"type">>, <<"groupchat">>}],
 		    children =
 			[#xmlel{name = <<"subject">>, attrs = [],
 				children = [{xmlcdata, Subject}]}]},
-    ejabberd_router:route(StateData#state.jid, JID, Packet).
+    ejabberd_router:route(jid:replace_resource(StateData#state.jid, Nick), JID,
+			  Packet).
 
 check_subject(Packet) ->
     case xml:get_subtag(Packet, <<"subject">>) of