* gnus-agent.el (gnus-agent-fetch-group): Modified to permit execution

* gnus-agent.el (gnus-agent-fetch-group): Modified to permit execution
in either the group or summary buffer.
New command "JS", in summary buffer, will fetch articles per the
group's category, predicate, and processable flags.
(gnus-agent-summary-fetch-series): Rewritten to call
gnus-agent-session-fetch-group once with all articles in the
series.
(gnus-agent-summary-fetch-group): Fixed bug and modified code to
return list of fetched articles.
(gnus-agent-fetch-articles): Split fetch list into sublists such
that the article buffer is only slightly larger than
gnus-agent-max-fetch-size.  Added unwind-protect to ensure that
the group's article alist is saved.
(gnus-agent-fetch-headers): The 'killed' and 'cached' marks no
longer result in the agent trying to fetch an article.
(gnus-agent-fetch-group-1): Can now be called in either the group
or summary buffer.  Removed the max-fetch-size code that I added
on 2002-12-13 as that capability is now part of
gnus-agent-fetch-articles.  Added code to update summary buffer.
When called in the group buffer, articles that can not be fetched
are AUTOMATICALLY MARKED AS READ.