title: django-simple-history, saving without historical record not working
body: <p>I am a big fan of django-simple-history, but I do not seem to be able to get "save_without_historical_record" to work properly when I use it inside the default save() method of a model.</p>
  
  <p>I have a model such as this</p>
  
  <pre><code>class NzPlasmid (models.Model):
      ...
      plasmid_map = models.FileField("Plasmid Map (max. 2 MB)", upload_to="temp/", blank=True)
      history = HistoricalRecords()
      ...
  </code></pre>
  
  <p>It has a custom save() method, which renames plasmid_map with the id of the newly created object. In order to do that, I save the object the first time to get its id, then use that to rename plasmid_map. I do not want to save a historical record for the first save, but only for the second. My custom save() method looks like this </p>
  
  <pre><code>def save(self, force_insert=False, force_update=False):
  
      self.skip_history_when_saving = True
      super(NzPlasmid, self).save(force_insert, force_update)
  
      ... some rename magic here ...
  
      del self.skip_history_when_saving
      super(NzPlasmid, self).save(force_insert, force_update)
  </code></pre>
  
  <p>which does not work, as I still get "duplicate" historical records everytime a plasmid is created.</p>
  
  <p>Thanks a lot in advance.</p>