'Returns information indicating if a db upgrade is necessary
and possible.
Returns one of the following:
(UPGRADE_NOT_NECESSARY, None)
(UPGRADE_NOT_POSSIBLE, "<reason>")
(UPGRADE_NECESSARY, None)'

def upgrade_info(self):

    if (self.version == self.VERSION):
        return (Database.UPGRADE_NOT_NECESSARY, None)
    return (Database.UPGRADE_NECESSARY, None)
