title: In my viewDidAppear, how do I know when it's being unwound by a child?
body: <p>When my child performs an unwind segue, my controller's viewDidAppear gets called.</p>
  
  <p>In this method (and this method alone, I need to know whether it was from an unwind or not)</p>
  
  <p>Note: the child is unwinding to the very first view controller, so this is an <strong>intermediate</strong> view controller, not the true root.</p>