Fifty years after her death at 29, Candy Darling – born Jimmy Slattery, of Massapequa, Long Island – is finally getting the star billing the Andy Warhol underground film star and transgender icon has long deserved.  As Cynthia Carr writes in her 418-page biography, Candy Darling: Dreamer, Icon, Superstar [Farrar, Straus and Giroux], Candy “was…