Use of super on old style class `Model`
I thought `Model` _was_ a new-style class?
 Oops, it seems that pyflake does not have enough intelligence to recognize these styles:

``` python
def with_metaclass(meta, base=object):
    return meta("NewBase", (base,), {})

class BaseModel(type):
    def __new__(cls, name, bases, attrs):
        return super(BaseModel, cls).__new__(cls, name, bases, attrs)

class Model(with_metaclass(BaseModel)):
    def save(self):
        pass

class MyModel(Model):
    def save(self): # [E1002, MyModel.save] Use of super on an old style class
        super(MyModel, self).save()
```

I got an pyflake error on overriding `Model#save` method:

> [E1002, MyModel.save] Use of super on an old style class

Here is the example:

``` python
# -*- coding: utf-8 -*-

from peewee import Model
class MyModel(Model):

    def save(self, *args, **kw):
        return super(MyModel, self).save(*args, **kw)

a = MyModel()
print MyModel.mro()
# [<class '__main__.MyModel'>, <class 'peewee.Model'>, <class 'peewee.NewBase'>, <type 'object'>]
```

Is it possible to turn `Model` class to a `new-style` class?
