Jem Aswad Senior Music EditorMariah Carey has always been about control: over her career, sure, but also over her extraordinary voice, which is her greatest asset as a performer. And that voice is in full bloom on “The Rarities,” her new compilation of previously unreleased and low-profile B-sides.Although releasing an album of rarities and outtakes can be like sharing baby pictures with the world, based on the evidence presented here, Mariah never really had much of an awkward stage.