Проблема решилась примерно так:
CREATE OR REPLACE FUNCTION test2(text)
RETURNS text AS
'
DECLARE
curs1 refcursor;
out_raw record;
BEGIN
OPEN curs1 FOR EXECUTE ''SELECT * FROM '' || quote_ident($1);
FETCH curs1 INTO out_raw;
CLOSE curs1;
RETURN out_raw.dir;
END;
'
LANGUAGE 'plpgsql';