title: Using gaetestbed within virtualenv
body: <p>I'd like to give GAE Testbed a try, but am running into the following error after completing the <a href="http://github.com/jgeewax/gaetestbed" rel="noreferrer">instructions on its homepage</a>. </p>
  
  <pre><code>$ nosetests --with-gae
  ...
  ImportError: No module named dev_appserver
  </code></pre>
  
  <p>I've confirmed that this happens in both a <em>virtualenv</em> and outside of one. </p>