title: celery doesn't find python-dateutil, although it is installed
body: <p>I have a virtualenv activated and I am running a command </p>
  
  <pre><code> celery -A dnslookup worker --loglevel=info
  </code></pre>
  
  <p>throws</p>
  
  <pre><code>Traceback (most recent call last):
  File "/Users/myuser/dev/project-backend-ENV/bin/celery", line 5, in &lt;module&gt;
  from pkg_resources import load_entry_point
  File "/Users/myuser/dev/project-backend-ENV/lib/python2.7/site-packages/setuptools-   0.6c11-py2.7.egg/pkg_resources.py", line 2607, in &lt;module&gt;
  File "/Users/myuser/dev/project-backend-ENV/lib/python2.7/site-packages/setuptools-0.6c11-py2.7.egg/pkg_resources.py", line 565, in resolve
  pkg_resources.DistributionNotFound: python-dateutil&gt;=1.5,&lt;2.0
  </code></pre>
  
  <p>but python-dateutil is installed in my virtualenv.</p>
  
  <p>How do I fix this?</p>