Even in hip-hop–a genre famous for auspicious debuts–Black Star, the first album from the team of Mos Def and Talib Kweli, stands out. It’s not just because these guys know their history (an update of Slick Rick’s classic “Children’s Story,” a fine jack of BDP’s “The P Is Free” on “Definition,” and shout-outs to 2Pac, Biggie, and the …