[Distutils] Confusing options error msg

[Randall Hopper]

Something else I noticed a bit earlier.  If you supply all three of:
packages, py_modules, and ext_modules, you get an error that says:

> setup.py build
running build
running build_py
error: build_py: supplying both 'packages' and 'modules' options is not allowed

It's not clear from the message which *_modules variable/variables are the
problem.  Based on PyNcurses's and Numerical's setup.py files, it's
apparent that py_modules is the culprit.  Removing it lets the build
continue.

That said, I do like how easy it appears it's going to be to build and
distribution module dists with the new DistUtils.  Copy setup.py, tweak,
and build.  Very nice.

Randall