switch to directed presence for pair requests

Testing between Google Talk and prosody, the directed IQ messages
were not received. Google Talk probably only relays them between
clients using the same account.

I first tried even more directed presence, with each client JID being sent
a separate presence, but that didn't work on Google Talk, particularly
it was ignored when one client sent it to another client using the same
account.

So, presence directed at the user@host of the client to pair with. Tested
working between Google Talk and prosody (in both directions), as well
as between two clients with the same account on Google Talk, and
two clients with the same account on prosody.

Only problem with this form of directed presence is that if I also use it
for git pushes, more clients than are interested in a push's data will
receive it. So I may need some better approach, or a hybrid between
directed IQ and directed presence.

Assistant/WebApp/Configurators/Pairing.hs

@@ -89,13 +89,11 @@ getStartXMPPPairR bid = do
 		(Just []) -> redirect StartPairR
 		(Just clients@((Client exemplar):_)) -> do
 			let samejid = basejid ourjid == basejid exemplar
-			liftAssistant $ forM_ clients $ \(Client jid) ->
-				unless (jid == ourjid) $ do
-					u <- liftAnnex getUUID
-					sendNetMessage $ PairingNotification
-						PairReq (formatJID jid) u
+			let account = formatJID $ basejid exemplar
+			liftAssistant $ do
+				u <- liftAnnex getUUID
+				sendNetMessage $ PairingNotification PairReq account u
 			pairPage $ do
-				let account = formatJID $ basejid exemplar
 				let name = buddyName exemplar
 				$(widgetFile "configurators/pairing/xmpp/inprogress")
   where