Method/attribute of same name of return type fail to typecheck

``` python
class A: pass

class B:
    def A(self) -> A: pass

B().A()
```

is a valid python code, but mypy

```
/tmp/asd.py: note: In function "A":
/tmp/asd.py:4: error: Invalid type "A"
```

It was found while typing [datetime.datetime.tzinfo](https://docs.python.org/3/library/datetime.html#datetime.datetime.tzinfo) which return a `tzinfo`.
