Django 1.5: Add suport to create and edit custom users. SiteUser is identical to auth.User

admin.py

from django.contrib import admin
from forms import SiteUserCreationForm, SiteUserChangeForm
from django.contrib.auth.admin import UserAdmin
from models import SiteUser


class SiteUserAdmin(UserAdmin):
    form = SiteUserChangeForm
    add_form = SiteUserCreationForm


admin.site.register(SiteUser, SiteUserAdmin)

forms.py

from django import forms
from django.contrib.auth.forms import UserCreationForm, UserChangeForm
from models import SiteUser

class SiteUserCreationForm(UserCreationForm):
    class Meta:
        model = SiteUser
        fields = ('username',)

    def clean_username(self):
        # Since User.username is unique, this check is redundant,
        # but it sets a nicer error message than the ORM. See #13147.
        username = self.cleaned_data["username"]
        try:
            SiteUser._default_manager.get(username=username)
        except SiteUser.DoesNotExist:
            return username
        raise forms.ValidationError(self.error_messages['duplicate_username'])


class SiteUserChangeForm(UserChangeForm):
    class Meta:
        model = SiteUser

models.py

from django.db import models
from django.contrib.auth.models import AbstractUser


class SiteUser(AbstractUser):
    photo = models.ImageField(upload_to='users/photos', null=True, blank=True, verbose_name='foto')
    cpf = models.CharField(max_length=11, null=True, blank=True, verbose_name='CPF')
    phone = models.CharField(max_length=200, null=True, blank=True, verbose_name='telefone')
    state = models.ForeignKey(State, null=True, blank=True, verbose_name='estado')
    cep = models.CharField(max_length=9, null=True, blank=True, verbose_name='CEP')
    is_student = models.BooleanField(default=False, verbose_name='é aluno?')

    class Meta:
        abstract = False
        verbose_name = 'Usuário'
        verbose_name_plural = 'Usuários'