title: Can't pip install virtualenv in OS X 10.8 with brewed python 2.7
body: <p>When trying to install virtualenv using a brewed python, I get the following error:</p>
  
  <pre><code>$ pip install virtualenv
  Requirement already satisfied (use --upgrade to upgrade): \
    virtualenv in /Library/Python/2.7/site-packages/virtualenv-1.9.1-py2.7.egg
  Cleaning up...
  </code></pre>
  
  <p>So clearly pip is somehow looking into the system python folder instead of the brewed one in /usr/local. How can I avoid this?</p>
  
  <p>The brew doctor finds no problems, and the path priority is set ok. </p>
  
  <p>I tried to remove the virtualenv package from the system python, 
  so I could install virtualenv with the brewed pip. 
  But then I could not create virtualenvs, as I got this error:</p>
  
  <pre><code>$ virtualenv datatransfer/
  Traceback (most recent call last):
    File "/usr/local/bin/virtualenv", line 5, in &lt;module&gt;
      from pkg_resources import load_entry_point
    File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 2603, in &lt;module&gt;
      working_set.require(__requires__)
    File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 666, in require
      needed = self.resolve(parse_requirements(requirements))
    File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 565, in resolve
      raise DistributionNotFound(req)  # XXX put more info here
  pkg_resources.DistributionNotFound: virtualenv==1.9.1
  </code></pre>
  
  <p>So I have not managed to avoid the system virtualenv.</p>
  
  <p>What I am doing wrong?</p>