title: "Unknown password hashing algorithm" when logging in with custom user
body: <p>I created a custom user model by inheriting from <code>django.contrib.auth.models.User</code>, and added it to my admin. When I create an instance from <code>MyUser</code> admin, I have two (related) problems:</p>
  
  <p>1- in the admin, the plain password (not uncrypted) is shown in the <code>password</code> field</p>
  
  <p>2- when I try to login in my admin with an instance of <code>MyUser</code>, I get</p>
  
  <pre><code>Unknown password hashing algorithm '&lt;mypassword&gt;'. Did you specify it in the PASSWORD_HASHERS setting    
  </code></pre>
  
  <p>is it a bug? how can I fix that? (I'm using Django 1.4.2)</p>
  
  <p><b>models.py</b></p>
  
  <pre><code>from django.contrib.auth.models import User
  
  class MyUser(User):
      number = models.IntegerField()
  </code></pre>
  
  <p><b>admin.py</b></p>
  
  <pre><code>class MyUserAdmin(admin.ModelAdmin):
      pass
  
  admin.site.register(MyUser, MyUserAdmin)
  </code></pre>
  
  <p><b>EDIT</b></p>
  
  <p>With the following the password is set properly, but when I want to modify some <code>MyUser</code> instance from the admin, the password is cleared and I have to set it again:</p>
  
  <pre><code>class MyUserAdminForm(forms.ModelForm):
  
      class Meta:
          model = MyUser
  
      def __init__(self, *args, **kwargs):
          super(MyUserAdminForm, self).__init__(*args, **kwargs)
          self.fields['password'].widget = forms.PasswordInput()
  
      def save(self, commit=True):
          user = super(MyUserAdminForm, self).save(commit=False)
          user.set_password(self.cleaned_data["password"])
          if commit:
              user.save()
          return user
  
  
  class MyUserAdmin(admin.ModelAdmin):
      form = MyUserAdminForm
  
  
  admin.site.register(MyUser, MyUserAdmin)
  </code></pre>