fix a recursive load error, Thanks to Richard Hansen for pointing this out

* lisp/ob-ditaa.el (org-ditaa-jar-path): Fix a recursive load error.

lisp/ob-ditaa.el

@@ -34,10 +34,14 @@
 ;; 3) we are adding the "file" and "cmdline" header arguments
 ;;
 ;; 4) there are no variables (at least for now)
+;;
+;; 5) it depends on a variable defined in org-exp-blocks (namely
+;;    `org-ditaa-jar-path') so be sure you have org-exp-blocks loaded
 
 ;;; Code:
 (require 'ob)
-(require 'org-exp-blocks)
+
+(defvar org-ditaa-jar-path) ;; provided by org-exp-blocks
 
 (defvar org-babel-default-header-args:ditaa
   '((:results . "file")