title: Django - forms error message showing twice when using validators
body: <p>I'm creating a contact form (therefore not using a model-based form) and I've come across the following problem, after adding a regex validator to my email field: the custom error message I've added is now being displayed twice.
  This happens when I enter an email such as 'something' (it doesn't match my regex nor has the default '@' symbol - if I add the '@' symbol, only one message shows up).</p>
  
  <p>I'm not sure, but I'm guessing django's default validation + my custom validation are responsible for that, so I'm wondering (if that's the problem), what I can do to prevent the same message from showing up twice.</p>
  
  <p>Thank you in advance!</p>
  
  <p>forms.py:</p>
  
  <pre><code>from django import forms
  from django.core.validators import RegexValidator   
  
  class ContactForm(forms.Form):
      full_name = forms.CharField(required=True)
      email = forms.EmailField(validators=[RegexValidator(regex=r'^\d+@([a-zA-Z0-9@-_]+)(\.[a-zA-Z0-9@-_]+)+\b')]
                              , error_messages={'invalid': 'This is my email error msg.'})
      message = forms.CharField(widget=forms.Textarea)
  </code></pre>
  
  <p>That 'This is my email error msg' is the one showing up repeatedly » eg: * This is my email error msg * This is my email error msg</p>
  
  <p>views.py:</p>
  
  <pre><code>def contact(request):
      form = ContactForm(request.POST or None)
      context = {"form":form}
  
      if form.is_valid():
          form_name = form.cleaned_data.get("full_name")
          form_email = form.cleaned_data.get("email")
          form_message = form.cleaned_data.get("message")
          subject = "Message from %s (%s)" % (form_name, form_email)
          from_email = form_email
          to_email = ['myemail',]
          contact_message = form_message
          send_mail(subject, contact_message, from_email, to_email, fail_silently=False)
          context = {"form":form,"thanks_msg": "Thank you!"}
  
      return render(request, 'contact.html', context)
  </code></pre>
  
  <p>template:</p>
  
  <pre><code>&lt;form action="" method="POST" class="form"&gt;  {% csrf_token %}
              {% for field in form %}
              &lt;div class="fields-container"&gt;
                  &lt;label class="label"&gt;{{ field.label }}&lt;/label&gt;
                  {{ field }}
              &lt;/div&gt; 
              &lt;p class="server-form-errors"&gt; {{ field.errors.as_text }} &lt;/p&gt;
              {% endfor %}
              &lt;button type="submit" id="form-button"&gt;Submit&lt;/button&gt;
          &lt;/form&gt;
  </code></pre>