Use the *new* setuptools, rather than distribute

This is a replacement to #2125.

This replaces the `distribute_setup.py` script with the new `ez_setup.py` script from setuptools 0.7.2 (i.e., what's supposed to be the "new new thing").

This seems to work in virtualenvs with distribute 0.6 or setuptools 0.7.2 installed, and therefore I *think* won't give problems.

@cgohlke: I'd love a sanity check on this in your Windows environment.