Create visibility overlays properly

* org.el (org-set-outline-overlay-data): Use outline-flag-region to make a
region invisible.  This ensures all necessary actions, especially adding
isearch-open-invisible property, are applied.

lisp/org.el

@@ -6626,8 +6626,7 @@ DATA should have been made by `org-outline-overlay-data'."
 	(widen)
 	(show-all)
 	(mapc (lambda (c)
-		(setq o (make-overlay (car c) (cdr c)))
-		(overlay-put o 'invisible 'outline))
+		(outline-flag-region (car c) (cdr c) t))
 	      data)))))
 
 ;;; Folding of blocks