add missing internal api for emacs 23.1

init.el

@@ -1,3 +1,13 @@
+;make .emacs.d support emacs 23.1 and above
+
+;only emacs 23.3 and above has string-prefix-p defined
+(if (not (fboundp 'string-prefix-p) )
+  (defun string-prefix-p (shorter longer)
+    (let ((n (mismatch shorter longer))
+	  (l (length shorter)))
+      (if (or (not n) (= n l)) l nil)))
+  )
+
 ;; -*- coding: utf-8 -*-
 (add-to-list 'load-path (expand-file-name "~/.emacs.d"))