instead of setting the action for the url, check if we have a channel listener.
this is a cleaner fix, and now the quoting back end doesn't need to know about
the nntp url.
the problem was when we ran the nntp url to get the message we weren't
calling OnDataAvailabe() on the channel listener. the reason is the channel
listener only got poked when ActionDisplayArticle was set as the action on
the nntp url. but this wouldn't be the case when we got run from the Quoting backend. I added a new action, and made sure to set it when running the url from the quoting back end, and then made sure the nntp backend did the right thing.
r=alecf, a=chofmann
