makemigrations produces incorrect path for inner classes

Description

When you define a subclass from django.db.models.Field as an inner class of some other class, and use this field inside a django.db.models.Model class, then when you run manage.py makemigrations, a migrations file is created which refers to the inner class as if it were a top-level class of the module it is in.
To reproduce, create the following as your model:
class Outer(object):
class Inner(models.CharField):
pass
class A(models.Model):
field = Outer.Inner(max_length=20)
After running manage.py makemigrations, the generated migrations file contains the following:
migrations.CreateModel(
name='A',
fields=[
('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
('field', test1.models.Inner(max_length=20)),
],
),
Note the test1.models.Inner, which should have been test1.models.Outer.Inner.
The real life case involved an EnumField from django-enumfields, defined as an inner class of a Django Model class, similar to this:
import enum
from enumfields import Enum, EnumField
class Thing(models.Model):
@enum.unique
class State(Enum):
on = 'on'
off = 'off'
state = EnumField(enum=State)
This results in the following migrations code:
migrations.CreateModel(
name='Thing',
fields=[
('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
('state', enumfields.fields.EnumField(enum=test1.models.State, max_length=10)),
],
),
This refers to test1.models.State, instead of to test1.models.Thing.State.