title: Django Rest Framework custom validation errors
body: <p>I'm trying to customize the default validation errors of DRF (3.x) for an account model.
  My goal is to write a validation function in order to send back a customized error message.</p>
  
  <p>I've tried the following:</p>
  
  <pre><code>class AccountSerializer(serializers.ModelSerializer):
      password = serializers.CharField(write_only=True, required=False)
  
      class Meta:
          model = Account
          fields = ('id', 'email', 'password',)
  
      def validate_password(self, value):
          """
          Validate Password.
          """
          if not value:
              raise serializers.ValidationError("Password cannot be empty!")
          elif len(value) &lt; 5:
              raise serializers.ValidationError("Password to short...")
          return value
  </code></pre>
  
  <p>The the length validation works fine, but the 'password is empty' validation is never thrown because the default error ('password', [u'This field may not be blank.']) is thrown before.</p>
  
  <p>Is there any option to disable default errors or to force validation by my custom function first?</p>
  
  <p>Thanks for help!</p>