This could/should/can be helped by clearing the build dir for Django in pip.
There is a bug for this, since version 1.1 see here for details
You can start checking for these folders here if you’re on OS X or unix like systems:
~/.pip
/tmp/pip-build-root (or pip-build-$USER, if you aren't running pip as root).
This is if you haven’t specified a new build folder when you installed the first version of Django.
Good luck!