* 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.

* gnus-sum.el (): Modified eval-when-compile to minimize
misleading compilation warnings.
(gnus-update-summary-mark-positions): Changed code to use
gnus-undownloaded-mark rather than gnus-downloaded-mark.

* nnheader.el (nnheader-insert-nov-file): Do not try to insert an
empty file as the parser assumes that the file isn't empty.

* nntp.el (nntp-send-string): The process-send-string call can,
because it performs I/O on the process, change the process' state
from open to closed.  If this happens, call nntp-report
immediately to report the broken connection.
(nntp-report): Rewritten to avoid needing a global variable to
determine the appropriate course of action.  Instead, two function
implementations are provided and the nntp-report function value is
bound to the appropriate implementation.
(nntp-retrieve-data): Moved nntp-report call to end of implementation.
(nntp-with-open-group): Now binds nntp-report's function cell
rather than binding gnus-with-open-group-first-pass.  Added a
condition-case to detect a quit during a nntp command.  When the
quit occurs, the current connection is closed as a fetch articles
request could have several megabytes queued up for reading.
(nntp-retrieve-headers): Bind articles to itself.  If
nntp-with-open-group repeats this command, I must have access to
the original list of articles.
(nntp-retrieve-groups): Ditto for groups.
(nntp-retrieve-articles): Ditto for articles.
(*): Replaced nntp-possibly-change-group calls to
nntp-with-open-group forms in all, but one, occurrance.
(nntp-accept-process-output): Bug fix. Detect when called with
null process.