Merge changes made in Gnus trunk.

Merge changes made in Gnus trunk.

auth.texi (Help for users): Login collection is "Login" and not "login".
gnus-sum.el (gnus-propagate-marks): Default to nil.
 (gnus-summary-exit): Kill the correct article buffer on exit from a `C-d' group.
gnus-start.el (gnus-use-backend-marks): Removed, since it duplicates gnus-propagate-marks.
gnus-sum.el (gnus-summary-exit-no-update): Restore the group conf before killing the buffers so that a non-full window conf gets handled correctly.
 (gnus-summary-exit): Ditto.
 (gnus-summary-read-group-1): Ditto.
nntp.el (nntp-retrieve-group-data-early): Reinstate the two-part async code again so that we can debug it properly.
message.el (message-reply): Take an optional switch-buffer parameter so that Gnus window confs are respected better.
auth-source.el (auth-source-secrets-search): Use `delete-dups', `append mapcar', and `butlast' instead of `remove-duplicates', `mapcan', and `subseq'.
 (auth-sources, auth-source-backend-parse, auth-source-secrets-search): Login collection is "Login" and not "login".
gnus-art.el (article-update-date-lapsed): Don't bug out when updating multiple headers.