Comedy fans had reason to be thankful the other night at Carolines on Broadway, where enigmatic Dave Chappelle popped in to see his former “Chappelle’s Show” cast mate Charlie Murphy perform. After a five-minute standing ovation, Chappelle kept the crowd in stitches with a 30-minute stand- up set. “Did you miss me?” he playfully asked the audience. “A lot’s changed since I was on TV. We have a black president now. Actually, Obama called me and asked me to help him with his campaign. He said he had two rules for me — don’t use the ‘N’ word, and stay off TV.” He went on, “Figures the first black president would run on a platform of only taxing the rich, and now I’m rich!” Chappelle returned to the club later that night to chat up another “Chappelle’s Show” alum, Paul Mooney, who was headlin ing the late show. Chappelle wrote the foreword to Mooney’s book, “Black Is the New White.”