fail on non-list solutions in setof/3 (#1553)

src/lib/builtins.pl

@@ -818,7 +818,8 @@ bagof(Template, Goal, Solution) :-
 :- non_counted_backtracking iterate_variants_and_sort/3.
 
 iterate_variants_and_sort([V-Solution0|GroupSolutions], V, Solution) :-
-    sort(Solution0, Solution),
+    sort(Solution0, Solution1),
+    Solution1 = Solution,
     (  GroupSolutions == [] -> !
     ;  true
     ).

tests/scryer/issues.rs

@@ -155,7 +155,7 @@ fn ignored_constraint() {
     run_top_level_test_no_args(
         "use_module(library(freeze)), freeze(X,false), X \\=a.\n\
          halt.",
-        "   freeze:freeze(X,user:false).\n",
+        "   freeze:freeze(X,false).\n",
     );
 }