improve plpgsql's EXECUTE 'select into' message with a hint

Hi,

while TFM says that we can use EXECUTE 'select ' INTO instead of the
non implemented EXECUTE 'select ... into ', the message in plpgsql
fails to say the same thing... seems like a HINT to me

-- 
Atentamente,
Jaime Casanova
Soporte y capacitación de PostgreSQL
Asesoría y desarrollo de sistemas
Guayaquil - Ecuador
Cel. +59387171157