* gnus-agent.el (gnus-agent-get-undownloaded-list): Now computes

	* gnus-agent.el (gnus-agent-get-undownloaded-list): Now computes
	gnus-newsgroup-unfetched, the list of articles whose headers have
	not been fetched from the server.

	* gnus-sum.el (gnus-summary-find-next): Removed undownloaded
	parameter as it never worked due to a bug.  Added check to prevent
	selection of any article in the gnus-newsgroup-unfetched list.
	(gnus-summary-find-prev): Added check to prevent selection of any
	article in the gnus-newsgroup-unfetched list.
	(gnus-summary-first-subject): Documented API. Modified
	implementation so that constraints are handled independently.
	Added check to prevent selection of any article in the
	gnus-newsgroup-unfetched list.
	(gnus-summary-first-unseen-subject): Updated parameters in
	gnus-summary-first-subject call to match new API.
	(gnus-summary-first-unseen-or-unread-subject): Ditto.
	(gnus-summary-catchup): Do not mark unfetched articles as read.