Create a db entry for this task file info
        and link it with a optional comment

        :param comment: a comment for the task file entry
        :type comment: str
        :returns: The created TaskFile django instance and the comment. If the comment was empty, None is returned instead
        :rtype: tuple of :class:`dj.models.TaskFile` and :class:`dj.models.Note`
        :raises: ValidationError, If the comment could not be created, the TaskFile is deleted and the Exception is propagated.

def create_db_entry(self, comment=''):
        """Create a db entry for this task file info
        and link it with a optional comment

        :param comment: a comment for the task file entry
        :type comment: str
        :returns: The created TaskFile django instance and the comment. If the comment was empty, None is returned instead
        :rtype: tuple of :class:`dj.models.TaskFile` and :class:`dj.models.Note`
        :raises: ValidationError, If the comment could not be created, the TaskFile is deleted and the Exception is propagated.
        """
        jbfile = JB_File(self)
        p = jbfile.get_fullpath()
        user = dj.get_current_user()
        tf = dj.models.TaskFile(path=p, task=self.task, version=self.version,
                                       releasetype=self.releasetype, descriptor=self.descriptor,
                                       typ=self.typ, user=user)
        tf.full_clean()
        tf.save()
        note = None
        if comment:
            try:
                note = dj.models.Note(user=user, parent=tf, content=comment)
                note.full_clean()
                note.save()
            except Exception, e:
                tf.delete()
                raise e
        return tf, note