LISTGROUP nearly broken with timecaf

[Marco d'Itri]

When a client sends a LISTGROUP command all timecaf of the storage class
containing the group are opened and scanned, every time. This makes the
command inusable. nnrpdcheckart is false.

I disabled the command in my newsreader (which now falls back to GROUP)
and entering a group now is a lot faster.

I think nnrpdcheckart should influence LISTGROUP too.

-- 
ciao,
Marco