org-compat: Use `define-advice' instead of `defadvice'

* lisp/org-compat.el (outline-flag-region):
(outline-next-visible-heading):
(outline-back-to-heading):
(outline-on-heading-p):
(outline-hide-sublevels):
(outline-toggle-children): Use `define-advice', remove redundant
interactive specs, and use `derived-mode-p' instead of `eq'
`major-mode'.

Suggested by Stefan Monnier.

lisp/org-compat.el

@@ -1456,69 +1456,58 @@ key."
 ;; Folding in outline-mode is not compatible with org-mode folding
 ;; anymore. Working around to avoid breakage of external packages
 ;; assuming the compatibility.
-(defadvice outline-flag-region (around outline-flag-region@fix-for-org-fold (from to flag) activate)
+(define-advice outline-flag-region (:around (oldfun from to flag) fix-for-org-fold)
   "Run `org-fold-region' when in org-mode."
-  (if (eq major-mode 'org-mode)
-      (setq ad-return-value (org-fold-region (max from (point-min)) (min to (point-max)) flag 'headline))
-    ad-do-it))
+  (if (derived-mode-p 'org-mode)
+      (org-fold-region (max from (point-min)) (min to (point-max)) flag 'headline)
+    (apply oldfun from to flag)))
 
-(defadvice outline-next-visible-heading (around outline-next-visible-heading@fix-for-org-fold (arg) activate)
+(define-advice outline-next-visible-heading (:around (oldfun arg) fix-for-org-fold)
   "Run `org-next-visible-heading' when in org-mode."
-  (interactive "p")
-  (if (eq major-mode 'org-mode)
-      (setq ad-return-value (org-next-visible-heading arg))
-    ad-do-it))
+  (if (derived-mode-p 'org-mode)
+      (org-next-visible-heading arg)
+    (apply oldfun arg)))
 
-(defadvice outline-back-to-heading (around outline-back-to-heading@fix-for-org-fold (&optional invisible-ok) activate)
+(define-advice outline-back-to-heading (:around (oldfun &optional invisible-ok) fix-for-org-fold)
   "Run `org-back-to-heading' when in org-mode."
-  (if (eq major-mode 'org-mode)
-      (setq ad-return-value
-            (progn
-              (beginning-of-line)
-              (or (org-at-heading-p (not invisible-ok))
-                  (let (found)
-	            (save-excursion
-	              (while (not found)
-	                (or (re-search-backward (concat "^\\(?:" outline-regexp "\\)")
-				                nil t)
-                            (signal 'outline-before-first-heading nil))
-	                (setq found (and (or invisible-ok (not (org-fold-folded-p)))
-			                 (point)))))
-	            (goto-char found)
-	            found))))
-    ad-do-it))
-
-(defadvice outline-on-heading-p (around outline-on-heading-p@fix-for-org-fold (&optional invisible-ok) activate)
+  (if (derived-mode-p 'org-mode)
+      (progn
+        (beginning-of-line)
+        (or (org-at-heading-p (not invisible-ok))
+            (let (found)
+	      (save-excursion
+	        (while (not found)
+	          (or (re-search-backward (concat "^\\(?:" outline-regexp "\\)")
+				          nil t)
+                      (signal 'outline-before-first-heading nil))
+	          (setq found (and (or invisible-ok (not (org-fold-folded-p)))
+			           (point)))))
+	      (goto-char found)
+	      found)))
+    (apply oldfun invisible-ok)))
+
+(define-advice outline-on-heading-p (:around (oldfun &optional invisible-ok) fix-for-org-fold)
   "Run `org-at-heading-p' when in org-mode."
-  (if (eq major-mode 'org-mode)
-      (setq ad-return-value (org-at-heading-p (not invisible-ok)))
-    ad-do-it))
+  (if (derived-mode-p 'org-mode)
+      (org-at-heading-p (not invisible-ok))
+    (apply oldfun invisible-ok)))
 
-(defadvice outline-hide-sublevels (around outline-hide-sublevels@fix-for-org-fold (levels) activate)
+(define-advice outline-hide-sublevels (:around (oldfun levels) fix-for-org-fold)
   "Run `org-fold-hide-sublevels' when in org-mode."
-  (interactive (list
-		(cond
-		 (current-prefix-arg (prefix-numeric-value current-prefix-arg))
-		 ((save-excursion (beginning-of-line)
-				  (looking-at outline-regexp))
-		  (funcall outline-level))
-		 (t 1))))
-  (if (eq major-mode 'org-mode)
-      (setq ad-return-value (org-fold-hide-sublevels levels))
-    ad-do-it))
-
-(defadvice outline-toggle-children (around outline-toggle-children@fix-for-org-fold () activate)
+  (if (derived-mode-p 'org-mode)
+      (org-fold-hide-sublevels levels)
+    (apply oldfun levels)))
+
+(define-advice outline-toggle-children (:around (oldfun) fix-for-org-fold)
   "Run `org-fold-hide-sublevels' when in org-mode."
-  (interactive)
-  (if (eq major-mode 'org-mode)
-      (setq ad-return-value
-            (save-excursion
-              (org-back-to-heading)
-              (if (not (org-fold-folded-p (line-end-position)))
-                  (org-fold-hide-subtree)
-                (org-fold-show-children)
-                (org-fold-show-entry 'hide-drawers))))
-    ad-do-it))
+  (if (derived-mode-p 'org-mode)
+      (save-excursion
+        (org-back-to-heading)
+        (if (not (org-fold-folded-p (line-end-position)))
+            (org-fold-hide-subtree)
+          (org-fold-show-children)
+          (org-fold-show-entry 'hide-drawers)))
+    (apply oldfun)))
 
 ;; TODO: outline-headers-as-kill