Conpherence - fix unread counts

Summary: we weren't updating the "latest seen transaction PHID" properly. do that and ONLY do it from the view handler so we know the user got a real good chance of actually seeing the message. also we weren't searching through the transactions correctly; fix that.

Test Plan: sent a test user some messages. noted the proper count of unread messages.

Reviewers: epriestley, chad

Reviewed By: chad

CC: aran, Korvin

Maniphest Tasks: T2399

Differential Revision: https://secure.phabricator.com/D4677

src/applications/conpherence/controller/ConpherenceViewController.php

@@ -49,8 +49,10 @@ final class ConpherenceViewController extends
     $this->setConpherence($conpherence);
 
     $participant = $conpherence->getParticipant($user->getPHID());
+    $transactions = $conpherence->getTransactions();
+    $latest_transaction = end($transactions);
     $write_guard = AphrontWriteGuard::beginScopedUnguardedWrites();
-    $participant->markUpToDate();
+    $participant->markUpToDate($latest_transaction);
     unset($write_guard);
 
     $header = $this->renderHeaderPaneContent();