The attached patch implements a command-line option to disable loading
of $HOME/.pydistutils.cfg.

After talking to Martin Loewis, I decided not to implement the override
part, because if it's a one-time thing you can just pass the settings on
the command line; and if you have two configurations you want to use
frequently, you can just use two user accounts.

The hard part was writing tests, since the existing code was untested
and is environment-sensitive. See the comments in the patch re. what I
still don't like about it. I would like to have a less evil test setup
and teardown, but I'm going on vacation tomorrow so I won't be able to
look at this again until April.