LIST OVERVIEW.FMT

I finally managed to stop dragging my feet about writing up a summary of the results and an analysis of the current uses of LIST OVERVIEW.FMT in NNTP and whether we should standardize it. Unfortunately, the results didn't really clarify things a great deal, but they did add some more information. The command is pretty rarely used, as far as I can see. I think it's an odd wart that we're probably better off without, but there's still that edge case of a news reader wanting to know what to expect from OVER responses that I can't quite dismiss.

We're down to the last three issues with the NNTP draft: this one, adding LIST HEADERS to the HDR extension (I think this has pretty much been decided at this point), and what to do about the 48x responses. I think the last one is also nearly resolved, so we should be just about done.