Marks don't pick up nested classes

Originally reported by: **Anonymous**

---

example:

```
#!python

@pytest.mark.a
class TestA:
    def test_b(self):
        assert True
    class TestC:
        def test_d(self):
            assert True
```

---

```
#!bash

$ py.test example.py -m a
```

only test_b is run. Not test_d

---
- Bitbucket: https://bitbucket.org/pytest-dev/pytest/issue/199
