Merge exclusives branch.

Auditors: benjy
Do a better job scrubbing PYTHONPATH.
Merge pull request #146 from wickman/wickman/better_pex_scrubbing

Do a better job scrubbing PYTHONPATH.
Merge remote-tracking branch 'origin/master'
fix includes
Merge pull request #147 from wickman/wickman/better_pex_scrubbing

fix includes from better_pex_scrubbing branch
force pex builder to use a safe pkg_resources
smdh
Merge pull request #148 from wickman/wickman/better_pex_scrubbing

monkeypatch pkg_resources.build_zipmanifest in an EggZipImport friendly way