unpack_iterable(): Add a missing DECREF in an error case.  Reported by
Armin Rigo (SF bug #488477).  Added a testcase to test_unpack_iter()
in test_iter.py.
diff --git a/Python/ceval.c b/Python/ceval.c
index fd602b0..b41ef5a 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -2796,6 +2796,7 @@
 		Py_DECREF(it);
 		return 1;
 	}
+	Py_DECREF(w);
 	PyErr_SetString(PyExc_ValueError, "too many values to unpack");
 	/* fall through */
 Error: