Romance is in the air at the National Zoo! Hot sloth bear love. Nineteen-year-old sloth bear Francois has returned to the D.C., after a stint at the Little Rock Zoo. There, our young Lothario sired two sets of cubs with Little Rock’s Nocona (who died in 2007). Now he’s back home at the National Zoo, where keepers want to hook him up with 15-year-old sloth bear Hana, whom he knew for five years before…