Go to combined inbox from notification for 2+ accounts (#2147265)

* The problem is that PendingIntents aren't updated when a notification
  is updated, so the changed extras when a 2nd account gets a new message
  aren't seen by MessageList when it's started up upon tapping the
  notification (it uses the extras from the 1st account to get a new
  message)
* The fix is to use the newish (cupcake) flag in the PendingIntent that
  causes the extras in the PendingIntent to be updated

Change-Id: Ia4ab14954b2c1413526016975216b2516372f2aa

src/com/android/email/service/MailService.java

@@ -677,7 +677,8 @@ public class MailService extends Service {
         }
 
         // prepare appropriate pending intent, set up notification, and send
-        PendingIntent pending = PendingIntent.getActivity(this, 0, intent, 0);
+        PendingIntent pending =
+            PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);
 
         Notification notification = new Notification(
                 R.drawable.stat_notify_email_generic,