returns current version of pgpm schema
        :return: tuple of major, minor and patch components of version

def get_pgpm_db_version(cls, cur, schema_name='_pgpm'):
        """
        returns current version of pgpm schema
        :return: tuple of major, minor and patch components of version
        """
        cls.set_search_path(cur, schema_name)
        cur.execute("SELECT _find_schema('{0}', '{1}')"
                    .format(schema_name, 'x'))
        # TODO: make it work with the way it's written below. currently throws error as func returns record
        # without column list
        # cur.callproc('_find_schema', [schema_name, 'x'])
        pgpm_v_ext = tuple(cur.fetchone()[0][1:-1].split(','))

        return pgpm_v_ext[2], pgpm_v_ext[3], pgpm_v_ext[4]