title: Django 1.6 error_messages in Modelform Meta class do not work
body: <p>I'm using Django 1.6.2 and the new meta options added in 1.6 version on ModelForms <a href="https://stackoverflow.com/a/21762860/1816323" title="related question">as mentioned in this question</a>, the errors on the forms are not displaying like i set them to.</p>
  
  <p>My code:</p>
  
  <p><strong>ModelForm</strong></p>
  
  <pre><code>class UserRegisterForm(forms.ModelForm):
      """A form for creating new users. Includes all the required
      fields, plus a repeated password."""
      password = forms.CharField(label='Password', widget=forms.PasswordInput)
  
      class Meta:
          model = MyUser
          fields = ('email','first_name','last_name')
  
          error_messages = {
              'email': {
                      'invalid': u"Hai",
                      'required': u"Sup",
              },
          }
  
      def save(self, commit=True):
          # Save the provided password in hashed format
          user = super(UserRegisterForm, self).save(commit=False)
          user.set_password(self.cleaned_data["password"])
          if commit:
              user.save()
          return user
  </code></pre>
  
  <p><strong>Template</strong></p>
  
  <pre><code>&lt;div class="form-group emailgroup {% if form.email.errors %}has-error has-feedback{% endif %}"&gt;
        &lt;label for="emailfield"&gt;Dirección de correo electrónico&lt;/label&gt;
        &lt;input type="email" class="form-control" id="emailfield" name="email" required placeholder="¿Cuál es tu dirección de correo electrónico?"&gt;
        {% if form.email.errors %}&lt;span class="glyphicon glyphicon-remove form-control-feedback"&gt;&lt;/span&gt;
        &lt;span class="help-block"&gt;{{ form.email.errors }}&lt;/span&gt;
        {% endif %}
  &lt;/div&gt;
  </code></pre>
  
  <p>Mind the following lines in the template where I print the errors of the field.</p>
  
  <pre><code>{% if form.email.errors %}&lt;span class="glyphicon glyphicon-remove form-control-feedback"&gt;&lt;/span&gt;
        &lt;span class="help-block"&gt;{{ form.email.errors }}&lt;/span&gt;
  {% endif %}
  </code></pre>
  
  <p>But I still get the predefined error message. What am I doing wrong?</p>