org-ascii.el: Fix escaping of underscores in links.

* org-ascii.el (org-export-as-ascii): Fix escaping of
underscores in links.

Thanks to Daniel Dehennin who reported this problem.

lisp/org-ascii.el

@@ -438,7 +438,9 @@ publishing directory."
 	      link (concat (match-string 1 line) path)
 	      type (match-string 2 line)
 	      desc0 (match-string 5 line)
-	      desc (or desc0 link))
+	      desc0 (replace-regexp-in-string "\\\\_" "_" desc0)
+	      desc (or desc0 link)
+	      desc (replace-regexp-in-string "\\\\_" "_" desc))
 	(if (and (> (length link) 8)
 		 (equal (substring link 0 8) "coderef:"))
 	    (setq line (replace-match