title: Error in Vim: "YouCompleteMe unavailable: This package should not be accessible on Python 3"
body: <p>When I attempt to use the YouCompleteMe plugin in vim, I get the following error: </p>
  
  <p><code>YouCompleteMe unavailable: This package should not be accessible on Python 3.  Either you are trying to run from the python-future src folder or your installation of python-future is corrupted</code></p>
  
  <p>However, I only get this error when I open vim within my virtual environment. It works fine when a virtualenv is not active. My guess is that YouCompleteMe is written in python 2, and for some reason can't see the python2 interpreter from inside the virtual environment, but I am not sure how to fix it. There does not appear to be a Stack Overflow question on the subject, but a similar issue came up in the ycm-users Google Group and went unanswered.</p>
  
  <p>I'm on Ubuntu 14.04, using vim version 7.4.</p>