title: virtualenv can't find python2
body: <p>I'm on a mac, which comes with python 2.7 installed, so I should have the required version.</p>
  
  <p>At least, I believe that's the problem. I'm getting an error when trying to run <code>make install</code> for a project, and getting the following error:</p>
  
  <pre><code>The executable python2 (from --python=python2) does not exist
  make: *** [bin/python] Error 3
  </code></pre>