avoids unorderable None, str when sorting dists on Python 3

Remove regression test for Distribute issue #318. The continuing relevance of this test is questionnaible, given that user installs of setuptools no longer imply user installs of other packages. Ref #360.

Remove comment that references a setup command, but even at the time it was committed, it's not duplicate code from anything in setuptools, and I'm unaware of what a setup command is.

Fix tox settings so they work