Re-activate test as it stopped failing

Switching py33-green to actually run w/ Python 3.3 helped. Leaving #8 open
though since it didn't make any sense. Waiting if it'll re-appear.

tests/test_threadlocal.py

@@ -126,13 +126,11 @@ def test_iter_works(self, D):
         d = D({'a': 42})
         assert ['a'] == list(iter(d))
 
-    # TODO: this fails on py33-green on Travis but *not* locally when
-    # unrelated code has been added.
-    # def test_non_dunder_proxy_works(self, D):
-    #     d = D({'a': 42})
-    #     assert 1 == len(d)
-    #     d.clear()
-    #     assert 0 == len(d)
+    def test_non_dunder_proxy_works(self, D):
+        d = D({'a': 42})
+        assert 1 == len(d)
+        d.clear()
+        assert 0 == len(d)
 
     def test_repr(self, D):
         r = repr(D({'a': 42}))