title: can't uninstall package with pip
body: <p>I have installed <code>pillow</code> package, and uninstall attempt with <code>sudo pip uninstall pillow</code> leads to this message:</p>
  
  <pre><code>Not uninstalling Pillow at /usr/lib/python2.7/dist-packages, owned by OS
  </code></pre>
  
  <p>Manual uninstall doesn't work, because pip writes down installed packages somewhere, successfuly blocking me from installing the package again.</p>