Enum of a NamedTuple-derived type leads to incompatible type error

This code:

``` python
from typing import NamedTuple
from enum import Enum

Foo = NamedTuple('Foo', [('bar', int)])

class MyEnum(Foo, Enum):
    CONSTANT = Foo(bar=1)

def f(x):
    # type: (MyEnum) -> None
    pass

f(MyEnum.CONSTANT)
```

leads to:

```
error: Argument 1 to "f" has incompatible type "test.MyEnum"; expected "MyEnum"
```
