[Distutils] patch distutils to look into .dist-info directories

[Daniel Holth]

Got it. https://bitbucket.org/dholth/distribute now includes the lazy
email.Parser() import and lazily imports 'markerlib' to implement
environment markers. BW compat should be easy as long as you don't use
.dist-info directories in your Python 2.3.

It implements the Provides-Extra: proposal to compute dependencies for
extras, important if you are converting existing packages to the 1.2
version of the metadata. Hopefully this is enough to convert a bunch
of existing packages over to .dist-info and Metadata 1.2 to see how it
goes, without having to affect setuptools users that much.