Fixed bug in completion

This one was hard to find. The first version of 
completion_mapfold used gather in all cases, so 
we had to return Env.empty.
The new version does not use gather in the normal
iteration so we have to return the same defnames
as the one given in argument.

compiler/heptagon/transformations/completion.ml

@@ -57,7 +57,7 @@ let block funs defnames b =
   let b, _ = Hept_mapfold.block funs Env.empty b in (*recursive call*)
   let added_eq = complete_with_last defnames b.b_defnames [] in
   { b with b_equs = b.b_equs @ added_eq; b_defnames = defnames }
-  , Env.empty
+  , defnames
 
 let eqdesc funs _ ed = match ed with
   | Epresent _ | Eautomaton _ | Eswitch _ ->