title: set an image background on a scrolling activity
body: <p>I'd like to change the background of a standard-generated <code>ScrollingActivity</code> (to an image).<br> Changing the background of the <code>content_scrolling.xml</code>  affects the area where I can put items in only.</p>
  
  <p>Is there a simple way I missed?<br>
  <em>(I am pretty surprised that I was not able to find an answer, so here we go)</em></p>
  
  <p><a href="http://i.stack.imgur.com/OdRk4.png" rel="nofollow">the blue background should be replaced by an image</a></p>