reactivate Thm.check_hyps, after adapting AFP/Datatype_Order_Generator (see AFP/b7e389b5765c);

--- a/src/Pure/goal.ML	Sat Jan 11 20:06:31 2014 +0100
+++ b/src/Pure/goal.ML	Sat Jan 11 21:39:21 2014 +0100
@@ -220,7 +220,7 @@
               (finish ctxt' st
                 |> Drule.flexflex_unique
                 |> Thm.check_shyps sorts
-                (* |> Thm.check_hyps (Context.Proof ctxt') *) (* FIXME *))
+                |> Thm.check_hyps (Context.Proof ctxt'))
               handle THM (msg, _, _) => err msg | ERROR msg => err msg;
           in
             if Unify.matches_list thy [Thm.term_of stmt] [Thm.prop_of res] then res