trim context for persistent storage;

--- a/src/Pure/raw_simplifier.ML	Wed Sep 02 22:02:31 2015 +0200
+++ b/src/Pure/raw_simplifier.ML	Wed Sep 02 22:14:44 2015 +0200
@@ -640,7 +640,7 @@
       val a = the (cong_name (head_of lhs)) handle Option.Option =>
         raise SIMPLIFIER ("Congruence must start with a constant or free variable", [thm]);
       val (xs, weak) = congs;
-      val xs' = AList.update (op =) (a, thm) xs;
+      val xs' = AList.update (op =) (a, Thm.trim_context thm) xs;
       val weak' = if is_full_cong thm then weak else a :: weak;
     in ((xs', weak'), procs, mk_rews, termless, subgoal_tac, loop_tacs, solvers) end);
 
@@ -1148,7 +1148,7 @@
                     (case cong_name h of
                       SOME a =>
                         (case AList.lookup (op =) (fst congs) a of
-                           NONE => appc ()
+                          NONE => appc ()
                         | SOME cong =>
      (*post processing: some partial applications h t1 ... tj, j <= length ts,
        may be a redex. Example: map (%x. x) = (%xs. xs) wrt map_cong*)