Visitors From Tonga -- Palu Vavau Tupou (left) and Veiongo Fakaua, cousins of Her Majesty Queen Salote of Tonga, broadcasting when they visited Britain recently. They were heard and seen in the British Broadcasting Corporation's "In Town Tonight", which is broadcast on both sound and television. When asked if they had been in Britain before Palu said "No, we have not been here. Not many people leave Tonga - my passport is number 72." Palu Vavau Tupou is Lady-in-waiting to Queen Salote of Tonga a