pypa/virtualenv — pull request #522 by qwcode (2014-01-02 19:40:06+00:00)
Title: ignore system installed pip/setuptools

fix for #521

previously, we installed pip/setuptools sdists using "python setup.py install", which ignores the global site (when using --system-site-packages)

but now, we're using pip itself to install wheels, so we need to use `--ignore-installed` (and luckily we fixed that option just recently)