Attached is a patch against gnus-sum.el to introduce the spam mark as
an exclusive (primary) mark.  The patch also creates a variable
gnus-newsgroup-spam-marked which will have the number of articles
marked as spam; a %h parameter for the summary format line is
introduced to show the number of articles marked as spam.  I know the
name of gnus-newsgroup-spam-marked is awkward, but I was trying to be
consistent with the other variable names (gnus-newsgroup-spam would
have been too vague).

This being the first time I've delved into the Gnus internals, I'd
appreciate feedback.  Simon Josefsson and Kai were very helpful in
getting me started.

I'm more or less back from my broken hand, so once this patch goes in
I will start on the spam.el functionality I discussed on the list
earlier.  Let me know if I should summarize my plan again.

Thanks
Ted