[IronPython] Generators are broken

[Sanghyeon Seo]

E:\IronPython-1.0-Beta1>IronPythonConsole
IronPython 1.0.2190 (Beta) on .NET 2.0.50727.42
Copyright (c) Microsoft Corporation. All rights reserved.
>>> def g():
...     yield 1
...
Traceback (most recent call last):
Exception: Object reference not set to an instance of an object.
>>>

Seo Sanghyeon