org-export-generic format: Fix compatibility issue with Emacs 23.

Patch by Wes Hardaker <wjhns209@hardakers.net>

contrib/ChangeLog

@@ -1,3 +1,8 @@
+2009-07-21  Wes Hardaker <wjhns209@hardakers.net>  (tiny change)
+
+	* lisp/org-export-generic.el (org-export-generic-format): Fix
+	compatibility issue with Emacs 23.
+
 2009-06-20  Carsten Dominik  <carsten.dominik@gmail.com>
 
 	* README: List new file org-export-generic.el

contrib/lisp/org-export-generic.el

@@ -1005,7 +1005,7 @@ REVERSE means to reverse the list if the plist match is a list
 	 subtype)
     (cond
      ((null prefixtype) "")
-     ((and len (characterp prefixtype))
+     ((and len (char-or-string-p prefixtype) (not (stringp prefixtype)))
       ;; sequence of chars
       (concat (make-string len prefixtype) "\n"))
      ((stringp prefixtype)