title: 'module' object has no attribute 'PY2'
body: <p>I am using ubuntu 14.04, was trying to install python-memcache. I have got an error like</p>
  
  <pre><code>Downloading/unpacking python-memcached
    Downloading python-memcached-1.53.tar.gz
  Cleaning up...
  Exception:
  Traceback (most recent call last):
    File "/usr/lib/python2.7/dist-packages/pip/basecommand.py", line 122, in main
      status = self.run(options, args)
    File "/usr/lib/python2.7/dist-packages/pip/commands/install.py", line 278, in run
      requirement_set.prepare_files(finder, force_root_egg_info=self.bundle, bundle=self.bundle)
    File "/usr/lib/python2.7/dist-packages/pip/req.py", line 1229, in prepare_files
      req_to_install.run_egg_info()
    File "/usr/lib/python2.7/dist-packages/pip/req.py", line 292, in run_egg_info
      logger.notify('Running setup.py (path:%s) egg_info for package %s' % (self.setup_py, self.name))
    File "/usr/lib/python2.7/dist-packages/pip/req.py", line 284, in setup_py
      if six.PY2 and isinstance(setup_py, six.text_type):
  AttributeError: 'module' object has no attribute 'PY2'
  
  Storing debug log for failure in /home/mani/.pip/pip.log
  </code></pre>
  
  <p>I am getting the same error when installing Django-celery, pymongo etc</p>