This year's 50th anniversary production of "HMS Pinafore" has an added attraction, the 45-minute ballet "Pineapple Poll." Gilbert wrote a book of verses, the "Bab Ballads," one of which was a precursor to Pinafore's story. In the late 1940s, Australian conductor Charles Mackerras set it to Sullivan's music from several of the operettas, and John Cranko, later artistic director of Stuttgart Ballet, choreographed it as "Pineapple Poll." Bernie Kwiram, Seattle G&S music director for the past three years, reorchestrated it for a smaller orchestra with Mackerras' permission