set negative XMPP presence priority

This should help prevent git-annex clients receiving messages that
were intended for normal clients they're sharing the account with.

Changed XMPP protocol use to always send chat messages directed at the
specific client, as the negative priority blocks less directed messages.

Assistant/Threads/XMPPClient.hs

@@ -137,7 +137,13 @@ decodeStanza selfjid s@(ReceivedMessage m)
 	| otherwise = [fromMaybe (Unknown s) (GotNetMessage <$> decodeMessage m)]
 decodeStanza _ s = [Unknown s]
 
-{- Waits for a NetMessager message to be sent, and relays it to XMPP. -}
+{- Waits for a NetMessager message to be sent, and relays it to XMPP.
+ -
+ - Chat messages must be directed to specific clients, not a base
+ - account JID, due to git-annex clients using a negative presence priority.
+ - PairingNotification messages are always directed at specific
+ - clients, but Pushing messages are sometimes not, and need to be exploded.
+ -}
 relayNetMessage :: JID -> Assistant (XMPP ())
 relayNetMessage selfjid = convert =<< waitNetMessage
   where
@@ -146,8 +152,13 @@ relayNetMessage selfjid = convert =<< waitNetMessage
 	convert (PairingNotification stage c u) = withclient c $ \tojid -> do
 		changeBuddyPairing tojid True
 		return $ putStanza $ pairingNotification stage u tojid selfjid
-	convert (Pushing c pushstage) = withclient c $ \tojid -> 
-		return $ putStanza $ pushMessage pushstage tojid selfjid
+	convert (Pushing c pushstage) = withclient c $ \tojid -> do
+		if tojid == baseJID tojid
+			then do
+				bud <- getBuddy (genBuddyKey tojid) <<~ buddyList
+				return $ forM_ (maybe [] (S.toList . buddyAssistants) bud) $ \(Client jid) ->
+					putStanza $ pushMessage pushstage jid selfjid
+			else return $ putStanza $ pushMessage pushstage tojid selfjid
 
 	withclient c a = case parseJID c of
 		Nothing -> return noop