A begrudging Mazel Tov from DCist to the city of San Diego is in order, as the Associated Press reports that Bai Yun, the San Diego Zoo's female panda, is definitely pregnant. Bai Yun has been put on "24-hour birth watch" after officials detected a fetus and fetal heartbeat through ultrasound images on July 18. More tests confirmed the pregnancy and the zoo made an official announcement yesterday. As you'll no doubt recall, Mei Xiang,......