use py26 compatible set syntax

Author: mrterry

tests/test_type.py

@@ -55,7 +55,7 @@ def test_positional_args():
     # thriftpy instantiates TPayload objects using positional args.
     # thriftpy.thrift.TException being the most notable example.
     # make sure that we don't break backwards compatiblity
-    s1 = Struct({1: 2}, {3, 4}, [5, 6])
-    assert s1.tdict == {1, 2}
-    assert s1.tset == {3, 4}
+    s1 = Struct({1: 2}, set([3, 4]), [5, 6])
+    assert s1.tdict == {1: 2}
+    assert s1.tset == set([3, 4])
     assert s1.tlist == [5, 6]