babel: Use `org-babel-map-src-blocks' in `org-babel-execute-buffer'

	* ob.el (org-babel-execute-buffer): Re-implement using
	`org-babel-map-src-blocks'

lisp/ob.el

@@ -570,15 +570,9 @@ results already exist."
 Call `org-babel-execute-src-block' on every source block in
 the current buffer."
   (interactive "P")
-  (save-excursion
-    (org-save-outline-visibility t
-      (goto-char (point-min))
-      (show-all)
-      (while (re-search-forward org-babel-src-block-regexp nil t)
-	(let ((pos-end (match-end 0)))
-	  (goto-char (match-beginning 0))
-	  (org-babel-execute-src-block arg)
-	  (goto-char pos-end))))))
+  (org-save-outline-visibility t
+    (org-babel-map-src-blocks nil
+      (org-babel-execute-src-block arg))))
 
 ;;;###autoload
 (defun org-babel-execute-subtree (&optional arg)