SFist loves us some old-school hip-hop, yo. We've got an entire library of classic movies, records and books on the subject. Which is why we were so excited to attend a park party hosted by Kevvy Kev on Sunday. Kev has been spinning the good stuff all over the bay for twenty years! Now that, friends, is old-school. To celebrate the twentieth anniversary of his radio show, Bang the Drum (6-9pm, Sundays, KZSU), he invited some of the top names in hip-hop from around the country....