avoid empty isabelletags.sty for the sake of arXiv;

--- a/lib/Tools/document	Mon Apr 29 17:08:57 2013 +0200
+++ b/lib/Tools/document	Mon Apr 29 17:17:20 2013 +0200
@@ -110,6 +110,7 @@
           ;;
       esac
     done
+    echo
   ) > isabelletags.sty
 }