rietveld: an attempt at pubsubhubbub

An attempt at adding pubsubhubbub support to Rietveld.
http://code.google.com/p/pubsubhubbub
http://code.google.com/p/rietveld/issues/detail?id=155

The server side of the protocol is trivial:
  1. add a <link rel="hub" href="hub-server"> tag to all
     feeds that will be pubsubhubbubbed.
  2. every time one of those feeds changes, tell the hub
     with a simple POST request.

I have tested this by adding debug prints to a local hub
server and checking that the server got the right publish
requests.

I can't quite get the server to work, but I think the bug
is not in my code.  I think that the server expects to be
able to grab the feed and see the feed's actual URL in
the link rel="self", but the default value for that drops
the :port from the URL, and I cannot for the life of me 
figure out how to get the Atom generator deep inside 
django not to do that, or even where it is doing that,
or even what code is running to generate the Atom feed.
(I thought I knew but I added some assert False statements
and it kept running!)

Ignoring that particular problem, I would appreciate
feedback on the right way to get the two values at
the top of feeds.py marked NOTE(rsc).