David Sedaris is a pioneer. Twenty-six years ago, the humorist busted through public radio’s polite veneer as a begrudging department store elf in "The SantaLand Diaries." Ten books later, Sedaris is a best-selling author who draws thousands of fans to his public readings. He writes frequently and candidly about his wisecracking, eccentric family. "Calypso," his newest collection of essays, is no exception. Virginia Prescott asked Sedaris about family, aging and writing about the negative when