title: Django TextField max_length validation for ModelForm
body: <p>Django does not respect the max_length attribute of TextField model field while validating a ModelForm.</p>
  <p>So I define a LimitedTextField inherited from the models.TextField and added validation bits similar to models.CharField:</p>
  <pre><code>from django.core import validators
  
  class LimitedTextField(models.TextField):
      def __init__(self, *args, **kwargs):
          super(LimitedTextField, self).__init__(*args, **kwargs)
          self.max_length = kwargs.get('max_length')
          if self.max_length:
              self.validators.append(validators.MaxLengthValidator(self.max_length))
  
      def formfield(self, **kwargs):
          defaults = {'max_length': self.max_length}
          defaults.update(kwargs)
          return super(LimitedTextField, self).formfield(**defaults)
  </code></pre>
  <p>But this still has no affect on ModelForm validation.</p>
  <p>What am I missing?</p>