[mod_python] Modifying publisher for sensible URLs

Hi!

> That functionality is already possible if you roll your own handler. 

Well, I think almost everything is possible when you do a lot on your own.

What I am focusing on is on is to provide a little extra functionality -
just for publisher.py - that makes mod_python more straight forward and easier
to develop programs for. (I do not think that such 15 lines of extra code
would blow up mod_python enormously. It would only affect the publisher.)