By DCist contributor W Jacarl Melton When Mos Def dropped the mic à la Randy Watson in Coming to America at the conclusion of Saturday’s 9:30 Club show, it was hard to tell if he was just being playful or if it was indicative of sentiments he harbored. A name like Mos Def, when announced to hip-hop heads or general music aficionados, is bound to create some buzz. This night was no different as…