title: DockPanel doesn't use whole space in ListBox, but outside it does
body: <p>In my Windows Phone application I'm using the DockPanel to align two buttons: one on the left side of the screen (PanoramaItem), second - on the right. 
  This code works well:</p>
  
  <pre><code>&lt;controls:PanoramaItem Header="page1"&gt;
     &lt;panel:DockPanel&gt;
        &lt;Button  Content="Right"  panel:DockPanel.Dock="Right"/&gt;
        &lt;Button  Content="Left"  panel:DockPanel.Dock="Left"/&gt;
     &lt;/panel:DockPanel&gt;
  &lt;/controls:PanoramaItem&gt;
  </code></pre>
  
  <p>But if I want dock buttons this way in ListBox - both align to the left :(</p>
  
  <pre><code>&lt;controls:PanoramaItem Header="page2"&gt;
     &lt;ListBox Margin="0,0,-12,0" HorizontalContentAlignment="Stretch" 
          ItemsSource="{Binding Collection}" Height="418" VerticalAlignment="Top"&gt;
       &lt;ListBox.ItemTemplate&gt;
          &lt;DataTemplate&gt;
             &lt;panel:DockPanel &gt;
                &lt;Button  Content="Right"  panel:DockPanel.Dock="Right"/&gt;
                &lt;Button  Content="Left"  panel:DockPanel.Dock="Left"/&gt;
             &lt;/panel:DockPanel&gt;
          &lt;/DataTemplate&gt;
       &lt;/ListBox.ItemTemplate&gt;
    &lt;/ListBox&gt;
  &lt;/controls:PanoramaItem&gt;
  </code></pre>