title: no module name datetime after ubuntu 13.04 upgrade
body: <p>Just did an upgrade from ubuntu 12.10 to 13.04 and getting this when running django site in virtualenv</p>
  
  <pre><code>(virtualenv)sysadmin@ubuntu:~/webapps/devsite/djangosite$ ./manage.py runserver
  Traceback (most recent call last):
    File "./manage.py", line 2, in &lt;module&gt;
      from django.core.management import execute_manager
    File "/home/sysadmin/webapps/devsite/virtualenv/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 7, in &lt;module&gt;
      from django.core.management.base import BaseCommand, CommandError, handle_default_options
    File "/home/sysadmin/webapps/devsite/virtualenv/local/lib/python2.7/site-packages/django/core/management/base.py", line 14, in &lt;module&gt;
      from django.utils.encoding import smart_str
    File "/home/sysadmin/webapps/devsite/virtualenv/local/lib/python2.7/site-packages/django/utils/encoding.py", line 4, in &lt;module&gt;
      import datetime
  ImportError: No module named datetime
  </code></pre>