NOW'S a chance for all Riverdance fans to really prove their loyalty to the show that got the world, nay the universe, doing the old haon-do- tri.Washington after a sell-out tour of both America and Australia. If you want to be present to cheer the return of the world's favourite jiggers, or indeed if you're one of the proud mammies and daddies, I'm afraid you'll have to be in Dublin airport at 6.20 a.m. this Tuesday. Now that's devotion.