Pip / distribute require setuptools 

Fixes pip install / upgrade error:

Exception:
Traceback (most recent call last):
  File "/usr/local/Cellar/python/2.7.8_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-1.5.6-py2.7.egg/pip/basecommand.py", line 122, in main
    status = self.run(options, args)
  File "/usr/local/Cellar/python/2.7.8_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-1.5.6-py2.7.egg/pip/commands/install.py", line 283, in run
    requirement_set.install(install_options, global_options, root=options.root_path)
  File "/usr/local/Cellar/python/2.7.8_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-1.5.6-py2.7.egg/pip/req.py", line 1439, in install
    requirement.rollback_uninstall()
  File "/usr/local/Cellar/python/2.7.8_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-1.5.6-py2.7.egg/pip/req.py", line 603, in rollback_uninstall
    self.uninstalled.rollback()
  File "/usr/local/Cellar/python/2.7.8_1/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-1.5.6-py2.7.egg/pip/req.py", line 1855, in rollback
    pth.rollback()