It was supposed to be a comeback of sorts, this strange, disjointed album, Sly Stone’s first release of new material since 1982. “I’m Back! Family & Friends” is part star-studded collaborations disc meant to evoke Carlos Santana’s career-reinvigorating “Supernatural,” part remix disc and part redone greatest hits, with a few new tracks tacked on near the end. Stone is one of pop’s most famous recluses, long dogged by rumors of drug abuse and strange behavior.