* gnus-art.el (gnus-narrow-to-page): Clear as well as set the value for

* gnus-art.el (gnus-narrow-to-page): Clear as well as set the value for
 gnus-page-broken.

* gnus-sum.el (gnus-summary-beginning-of-article): Use gnus-break-pages
 instead of gnus-page-broken.
(gnus-summary-end-of-article): Use gnus-break-pages instead of
 gnus-page-broken;
 narrow to the end of a page beforehand.
(gnus-summary-toggle-header): Use gnus-break-pages instead of
 gnus-page-broken;
 remove delimiter buttons unless gnus-break-pages is non-nil.