title: Django GenericIPAddress field is not validating input
body: <p>Hi I have the following Django model</p>
  
  <pre><code>class AccessPointIPAddress(models.Model):
      '''Model for storing AccessPoint IP Addresses.'''
      ap = models.ForeignKey(AccessPoint, related_name='ip_addresses')
      ip_address = models.GenericIPAddressField(protocol='IPv4')
      datetime = models.DateTimeField(auto_now_add=True)
  
      class Meta:
          ordering = ['datetime']
          get_latest_by = 'datetime'
  </code></pre>
  
  <p>And I am assuming that django's <code>GenericIPAddressField</code> does some string validation that a string is indeed a valid IP Address. I also read django's source and it does have some validation functions tied to <code>GenericIPAddressField</code></p>
  
  <p>But when I try to run this on django's shell:</p>
  
  <pre><code># Assume that *ap* is a valid AccessPoint instance
  # Notice ip_address IS NOT A VALID IP ADDRESS
  &gt;&gt; AccessPointIPAddress.objects.create(ap=ap, ip_address='xxxxxx123123----')
  &lt;AccessPointIPAddress: ap xxxxxx123123---- 2015-05-18 12:39:25.491811&gt;
  </code></pre>
  
  <p>I am expecting that it should raise some kind of ValueError or validation error since the given ip-address <code>xxxxxx123123----</code> is not a valid ip address.</p>
  
  <p>Am I missing something here? Or is this part of django broken? Currently using Django 1.6.5</p>