Feature request: display group parameter

[Wesley.Hardaker@sphys.unil.ch]

Background:  

`display'
     Elements that look like `(display . MODE)' says which articles to
     display on entering the group.  Legal values are:

     `all'
          Display all articles, both read and unread.

     `default'
          Display the default visible articles, which normally includes
          unread and ticked articles.

I use 'display all' in a few of my groups, like my inbox for
example...  I want to show read messages as well as new ones, for
somewhat obvious reasons...

What I *don't* want to see though is the Expired articles, because,
well, I've deleted them!  (Granted I don't want them totally gone for
2 weeks just in case..., but I don't want to see them unless I request
it).

Therefore, we need a new MODE parameter, say something like 'current'
or 'pre-expired' or (uhhh...) 'exactly-what-wes-wants' or something to
that effect...  It would of course be 'default' + 'read'...

Wes