org.el (org-mode): Use `org-back-to-heading' and `org-end-of-subtree' for C-M-a and C-M-e

* org.el (org-mode): Use `org-back-to-heading' and
`org-end-of-subtree' for C-M-a and C-M-e.

This partially reverts commit 76fa97922.

Thanks to Leo Liu for reporting this.

lisp/org.el

@@ -5377,8 +5377,9 @@ The following commands are available:
   ;; Comments.
   (org-setup-comments-handling)
   ;; Beginning/end of defun
-  (org-set-local 'beginning-of-defun-function 'org-backward-element)
-  (org-set-local 'end-of-defun-function 'org-forward-element)
+  (org-set-local 'beginning-of-defun-function 'org-back-to-heading)
+  (org-set-local 'end-of-defun-function
+		 (lambda () (interactive) (org-end-of-subtree nil t)))
   ;; Next error for sparse trees
   (org-set-local 'next-error-function 'org-occur-next-match)
   ;; Make sure dependence stuff works reliably, even for users who set it