(gnus-article-send-map): New keymap for S prefix keys; bind SW key to

(gnus-article-send-map): New keymap for S prefix keys; bind SW key to
 gnus-article-wide-reply-with-original;
 set default binding to gnus-article-read-summary-send-keys.
(gnus-article-read-summary-keys): Fix the order of keys;
 display continuation keys correctly in the echo area;
 describe bindings correctly when keys end with C-h.
(gnus-article-read-summary-send-keys): New function.
(gnus-article-describe-key, gnus-article-describe-key-briefly): Work for
 gnus-article-read-summary-send-keys;
 display continuation keys correctly in the echo area.
(gnus-article-reply-with-original): Ignore prefix argument.
(gnus-article-wide-reply-with-original): New function.