title: GCM (Google Cloud Messaging) not sending error on uninstall of app
body: <p>I'm trying to migrate from C2DM to GCM, and it mostly works just fine. C2DM used to handle uninstalls of the app very well by sending a NotRegistered error when the user uninstalled the app. GCM supposedly does this as well (albeit not guaranteed). However, it doesn't seem to be working. After sending multiple GCM notifications to a phone which has uninstalled the app, it still keeps responding with a normal "id=..." response.</p>
  
  <p>Has anyone else come across this problem? If so, how did you solve it?</p>