title: listbox.SetSelected(int, true) is not working in Windows Phone 7
body: <p>In my Windows Phone 7 app, I have a listbox in the Xaml with some stuff in it.</p>
  
  <p>Then in the C# code, I tried</p>
  
  <pre><code>listbox.SetSelected( anInteger, true);
  </code></pre>
  
  <p>Only it didn't work.</p>
  
  <p>So am I doing something wrong? How do I select an item from the listbox with an integer in Windows Phone 7 with C#?</p>