(gnus-summary-search-article): Treat and recenter the article when touchdown;

(gnus-summary-search-article): Treat and recenter the article when touchdown;
popup the article buffer if it is disappeared.
(gnus-summary-search-article-highlight-matched-text): Treat the article before
highlighting; use old style backquote syntax.
(gnus-summary-search-article-position-point): Fix the beginning position;
use old style backquote syntax.
(gnus-summary-select-article): Undo the last change.
(gnus-summary-display-article): Bind `gnus-summary-search-article-matched-data'
in the article buffer locally.  It is moved from `gnus-summary-select-article'.