[IronPython] Crash on method call

[Seo Sanghyeon]

With following code, IronPython 0.9.5 crashes with the message
"Unhandled Exception: no value for arg".

class C:
    def foo(self, arg, bar):
        pass

obj = C()
obj.foo(None, bar=1)

Above testcase was reduced from Python standard library's optparse.py,
line 1120, in Python 2.4.2.

Seo Sanghyeon