Coco Framboise performed with a giant telephone, Scarlett Diamond twirled an ostrich feather parasol. Yet London's third international burlesque festival, held last weekend, was far from sleazy. Audiences were 50-50 men and women, the former swellegant in spats, the latter in halter-neck dresses and many a small fascinator and veil. In fact, everything harked back to the Twenties, Thirties and Forties - to an imagined softer, coyer time.