less ghc-specific pragma

--- a/src/Tools/Code/code_haskell.ML	Mon Nov 29 11:38:59 2010 +0100
+++ b/src/Tools/Code/code_haskell.ML	Mon Nov 29 11:39:00 2010 +0100
@@ -356,7 +356,7 @@
             val _ = Isabelle_System.mkdir (Path.dir filepath);
           in
             (File.write filepath o format [] width o Pretty.chunks2)
-              [str "{-# OPTIONS_GHC -fglasgow-exts #-}", content]
+              [str "{-# LANGUAGE ScopedTypeVariables #-}", content]
           end
       | write_module width NONE (_, content) = writeln (format [] width content);
   in