title: Catch PyGTK TreeView reorder
body: <p>I have a simple <code>gtk.TreeView</code> with a <code>gtk.ListStore</code> model and <code>set_reorderable(True)</code>, I want to catch the signal/event emited when the user reorder through drag&amp;drop the list, but the documentation does not help much: </p>
  
  <p><em>"The application can listen to these changes by connecting to the model's signals"</em></p>
  
  <p>So I tried to connect the model (ListStore) signals... but surprise! ListStore has no signals, so you are dispatched to TreeModel signals, then I tried to connect with the TreeModel "rows-reordered" signal with no lucky.</p>
  
  <p>How should I catch the list reorder performed by the user?</p>