title: Django makemigrations doesn't work
body: <p>Something wrong went with Django makemigrations, the code like below:</p>
  
  <pre><code>class User(AbstractBaseUser, PermissionsMixin):
  
      nickname = models.CharField(max_length=30, blank=True, verbose_name=u'')
      is_staff = models.BooleanField(default=False, verbose_name=u'')
      is_active = models.BooleanField(default=True, verbose_name=u'')
  
      objects = UserManager()
  </code></pre>
  
  <p>When I run <code>python manage.py makemigrations</code> , the field <code>is_staff</code> doesn't show up in the migration file. I don't know why this field disappears. But if I change the name to <code>is_aa</code>, it shows right.</p>
  
  <p>The migration file is:</p>
  
  <pre><code>class Migration(migrations.Migration):
  
  initial = True
  
  dependencies = [
      ('auth', '0008_alter_user_username_max_length'),
  ]
  
  operations = [
      migrations.CreateModel(
          name='User',
          fields=[
              ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
              ('password', models.CharField(max_length=128, verbose_name='password')),
              ('last_login', models.DateTimeField(blank=True, null=True, verbose_name='last login')),
              ('is_superuser', models.BooleanField(default=False, help_text='Designates that this user has all permissions without explicitly assigning them.', verbose_name='superuser status')),
              ('nickname', models.CharField(blank=True, max_length=30, verbose_name='\u6635\u79f0')),
              ('is_active', models.BooleanField(default=True, verbose_name='\u662f\u5426\u6709\u6548')),
              ('groups', models.ManyToManyField(blank=True, help_text='The groups this user belongs to. A user will get all permissions granted to each of their groups.', related_name='user_set', related_query_name='user', to='auth.Group', verbose_name='groups')),
              ('user_permissions', models.ManyToManyField(blank=True, help_text='Specific permissions for this user.', related_name='user_set', related_query_name='user', to='auth.Permission', verbose_name='user permissions')),
          ],
          options={
              'db_table': 'user',
          },
          managers=[
              ('objects', apps.api.user.models.UserManager()),
          ],
      ),
  </code></pre>