Make superscripts produce a ^ in the output, instead of _

* ox-ascii.el (org-ascii-superscript): Change _ to ^ in the output.

Reported by Suvayu Ali: http://thread.gmane.org/gmane.emacs.orgmode/86014

lisp/ox-ascii.el

@@ -1594,8 +1594,8 @@ contextual information."
 CONTENTS is the contents of the object.  INFO is a plist holding
 contextual information."
   (if (org-element-property :use-brackets-p superscript)
-      (format "_{%s}" contents)
-    (format "_%s" contents)))
+      (format "^{%s}" contents)
+    (format "^%s" contents)))
 
 
 ;;;; Strike-through