title: No module named 'pip._vendor.cachecontrol'
body: <p>Running pip on OSX gives the following error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "/usr/local/bin/pip", line 9, in &lt;module&gt;
      load_entry_point('pip==6.0.6', 'console_scripts', 'pip')()
    File "build/bdist.macosx-10.10-x86_64/egg/pkg_resources/__init__.py", line 519, in load_entry_point
    File "build/bdist.macosx-10.10-x86_64/egg/pkg_resources/__init__.py", line 2630, in load_entry_point
    File "build/bdist.macosx-10.10-x86_64/egg/pkg_resources/__init__.py", line 2310, in load
    File "build/bdist.macosx-10.10-x86_64/egg/pkg_resources/__init__.py", line 2316, in resolve
    File "/usr/local/Cellar/python/2.7.7_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-6.0.6-py2.7.egg/pip/__init__.py", line 15, in &lt;module&gt;
      from pip.vcs import git, mercurial, subversion, bazaar  # noqa
    File "/usr/local/Cellar/python/2.7.7_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-6.0.6-py2.7.egg/pip/vcs/mercurial.py", line 11, in &lt;module&gt;
      from pip.download import path_to_url
    File "/usr/local/Cellar/python/2.7.7_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-6.0.6-py2.7.egg/pip/download.py", line 36, in &lt;module&gt;
      from pip._vendor.cachecontrol import CacheControlAdapter
    File "/usr/local/Cellar/python/2.7.7_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-6.0.6-py2.7.egg/pip/_vendor/__init__.py", line 81, in load_module
      raise ImportError("No module named '%s'" % (name,))
  ImportError: No module named 'pip._vendor.cachecontrol'
  </code></pre>
  
  <p>Any idea what am I doing wrong?</p>