N816 considers generator/list comprehensions to be globally scoped

The following will trigger N816 twice:

```python
(someVar1 == 8 for someVar1 in [])
[someVar2 == 8 for someVar2 in []]
```

N816 is explained as "mixedCase variable in global scope".

But are they really globals? Should there not be a new error code Nxyz for this? Or is it a limitation or shortcut in pep8-naming that leads to this behavior?

Version: 0.14.1