Multiple article buffers

[Lars Magne Ingebrigtsen <larsi@ifi.uio.no>]

I've now added multiple article buffers, and it seems to work ok.
It's off by default; `gnus-single-article-buffer' is the variable to
use.  Seems kinda neat, actually, having two summary buffers and two
article buffers open at the same time...  Even useful, perhaps.  :-)

I thought I'd finally write that "multiple directory nnml" thing,
where nnml would look into sub-directories called "2101-2200", and
look at the overview file there and stuff.  But it seems to me that
this'd be a totally new backend since not much of the code could be
shared between the two different methods.  Or perhaps...  (This just
occurred to me...)  We could have an "nnmulti" backend that combined
several groups (of random formats) into a single group.  A but like
nnvirtual, but not at all, I think.  This would be useful for, say,
combining several digests into one biiig group...  Hm.  

-- 
(domestic pets only, the antidote for overdose, milk.)
  larsi@ifi.uio.no * Lars Ingebrigtsen