We should devendor packaging from setuptools. From IRC:
<dstufft> By the way, I'm pretty sure that
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=814397 is because
pip unbundles and the latest python-pkg-resources doesn't
<dstufft> (now that I actually look at setuptools)
<dstufft> so pip is using packaging.version.Version and pkg_resources is
giving it pkg_resources._vendor.packaging.version.Version [16:48]
