title: Pop to root view controller in app delegate
body: <p>I have an app that someone logs into and if they launch it after sending it to the background for more than 10 minutes I pop up a nice little "session expired" alert and send them to the root view controller (login page). </p>
  
  <p>Everything works great but I don't know how to pop to the root view controller in my navigation controller stack from the app delegate's applicationWillEnterForeground: method.</p>
  
  <p>I tried saving off the navigationController onto an appDelegate variable but I wonder if the app is in the background for several days, if iOS starts freeing some variables, as I get an error in this method at that time.</p>
  
  <p>Any ideas?</p>