[Twisted-Python] very weird 16.4 upgrade breakage

On Mimic, the requires.io PR that upgraded us to Twisted 16.4 broke the build. It did so in a really weird way: https://travis-ci.org/rackerlabs/mimic/jobs/156439316 Specifically, our mac app CI tests failed like so: File "pkg_resources/extern/__init__.pyc", line 61, in load_module exceptions.ImportError: The 'appdirs' package is required; normally this is bundled with this package so if you get this warning, consult the packager of your distribution. Any idea why 'appdirs' might suddenly become a hard dependency of pkg_resources, but only in the py2app bundle? Did something change about the way we referenced dependencies? -glyph