Testing with current tip in hg (pre 1.4.20) and python 2.7.2 and I get the issue
when running demo.py and trying to csv export something with a column that does 
not exist. I can see it with curl and a webbrowser.

However I don't like the resulting error message, somehow the
expection.NotFound does not propagate a message up.
I believe that ./cgi/client.py will actually reraise raise NotFound(e)
but I haven't tracked it to roundup_server. So what do we need to change
to get the message out that we could not find that column?