At a moment when no one knew whether David Bowie was a transvestite, provocateur, folk singer or space alien, the then 24-year-old released an album that slyly capitalized on the confusion. “Life on Mars?” placed him in deep space, while a trilogy to his idols (“Andy Warhol,” “Song for Bob Dylan” and “Queen Bitch” — for Lou Reed) clarified his earthbound ambition to be a boho poet with prodigal style. Changes, meanwhile, proved he could write a great pop song about who really (maybe) was.