Checks whether a table for the given model class already exists.
        Note that this only checks for existence of a table with the expected name.

def does_table_exist(self, model_class):
        '''
        Checks whether a table for the given model class already exists.
        Note that this only checks for existence of a table with the expected name.
        '''
        sql = "SELECT count() FROM system.tables WHERE database = '%s' AND name = '%s'"
        r = self._send(sql % (self.db_name, model_class.table_name()))
        return r.text.strip() == '1'