DOC: update comments for ``run_setup``
BF: fix bugs in distutils.core

Github-user Vickor pointed out that `run_setup` is distutils is awaiting
some patches:

https://github.com/MacPython/bdist_mpkg/issues/1
http://bugs.python.org/issue18970

Apply these patches, add some tests.  Closes gh-1
Merge pull request #5 from matthew-brett/run_setup-fixes

MRG: Run setup fixes

Apply fixes to distutils.core routine in Python. Thanks Vickor for pointing these out.