'Create a new article revision when the edit form is valid
(does not concern any sidebar forms!).'

def form_valid(self, form):

    revision = models.ArticleRevision()
    revision.inherit_predecessor(self.article)
    revision.title = form.cleaned_data[u'title']
    revision.content = form.cleaned_data[u'content']
    revision.user_message = form.cleaned_data[u'summary']
    revision.deleted = False
    revision.set_from_request(self.request)
    self.article.add_revision(revision)
    messages.success(self.request, _(u'A    new    revision    of    the    article    was    successfully    added.'))
    return self.get_success_url()
