Hello!

I am trying to solve the following problem: Using nnvirtual groups that
are made up of several nntp newsgroups I would like to limit by
`Newsgroups' when in the nnvirtual. From reading the code, it appears
that this means I cannot use NOV because then the extra headers list
won't be generated. I can set `nov-is-evil' and this works. Except when
I am also using agent mode, in which case it will always use the NOV.

The below patch is a work in progress and doesn't entirely work yet, but
I wanted to share it early before I spend more time on it.

The following questions have come up for me:

1) Is there a different way to solve this problem? Specifically, is
there a better way to limit by newsgroup when in an nnvirtual group?
2) Is it possible to set `nntp-nov-is-evil' as a group parameter? It
looks like header retrieval may be too early for this and I may need to
use a hook?
3) How would this approach interact with the local cache? I have not
looked at this path yet.

Thanks!