avoid polymorphic equality;

--- a/src/Pure/Isar/outer_parse.ML	Mon Oct 08 18:13:08 2007 +0200
+++ b/src/Pure/Isar/outer_parse.ML	Mon Oct 08 18:13:09 2007 +0200
@@ -159,7 +159,7 @@
 
 fun reserved x =
   group ("Reserved identifier " ^ quote x)
-    (Scan.one (T.ident_with (equal x)) >> T.val_of);
+    (Scan.one (T.ident_with (fn y => x = y)) >> T.val_of);
 
 val semicolon = $$$ ";";