Send the activation email. The activation key is the username,
        signed using TimestampSigner.

def send_activation_email(self, user):
        """
        Send the activation email. The activation key is the username,
        signed using TimestampSigner.

        """
        activation_key = self.get_activation_key(user)
        context = self.get_email_context(activation_key)
        context.update({
            'user': user
        })
        subject = render_to_string(self.email_subject_template,
                                   context)
        # Force subject to a single line to avoid header-injection
        # issues.
        subject = ''.join(subject.splitlines())
        message = render_to_string(self.email_body_template,
                                   context)
        user.email_user(subject, message, conf.get('DEFAULT_FROM_EMAIL'))