BUG: re-initialize the master working set
BUG: re-initialize the master working set

In some cases (specifically when pip imports this module in a virtualenv),
pkg_resources can already be imported, causing setuptools to load
entry_points from an older version. Here, we re-initialize the master
working set to fix the case where the entry points from an older
setuptools are loaded.
pypa/setuptools,pypa/setuptools,pypa/setuptools