title: Grouping layers with groext - openlayer overlays menu
body: <p>i can't find out how to grup layers like in this example
  <a href="http://dev.openlayers.org/releases/OpenLayers-2.10/examples/controls.html" rel="nofollow">http://dev.openlayers.org/releases/OpenLayers-2.10/examples/controls.html</a>
  press the upper + button</p>
  
  <p>as you can see there's a checkbox and two radio buttons</p>
  
  <p>anyone knows a way to group layers so that they are displayed under the same group and it's possible to choose only one among them? (radio button)</p>
  
  <p>thank you</p>