Issue #2335: Backport set literals syntax from Python 3.x.
diff --git a/Python/symtable.c b/Python/symtable.c
index d782a19..5e735cc 100644
--- a/Python/symtable.c
+++ b/Python/symtable.c
@@ -1211,6 +1211,9 @@
 		VISIT_SEQ(st, expr, e->v.Dict.keys);
 		VISIT_SEQ(st, expr, e->v.Dict.values);
 		break;
+        case Set_kind:
+		VISIT_SEQ(st, expr, e->v.Set.elts);
+		break;
         case ListComp_kind:
 		VISIT(st, expr, e->v.ListComp.elt);
 		VISIT_SEQ(st, comprehension, e->v.ListComp.generators);