title: Issue getting viewState's selected child's id in flex 4
body: <p>I'm transitioning a flex 3 application to flex 4.  There was AS code in the flex 3 app that worked:</p>
  
  <pre><code>var myCurrentSelectedChild:String = myViewStack.selectedChild.id;
  </code></pre>
  
  <p>Now, in flash builder and flex 4.5, it throws the error - "-1119: Access of possibly undefined property id through a reference with static type mx.core:INavigatorContent".  I'm trying to get the viewStack's selected child's id.  </p>