feed auto-discovery

I added feed auto-discovery to CastSampler.com today. It was pretty
easy using the feedfinder.py module, except for one small
problem. Something about the timelimit() decorator in that module
causes problems with django or mod_python (probably
mod_python). When timelimit() is enabled, the finder either produces
no URLs at all or an exception about “unmarshalling code objects” in a
“restricted execution environment.” It works great in my development
environment, which does not use mod_python. To get it to work in
production, I disabled the timelimit() decorator. I hope that does not
come back to bite me in the future.