On Monday, Peter Salovey, president of Yale University, strode down the tree-lined streets of downtown New Haven, garbed in voluminous robes, a massive pendant, and a velvet cap with a gold, dangling tassel. Before him walked a scowling bulldog puppy that strained against its leash. Handsome Dan XVIII, the university’s mascot, was processing in his first commencement, and both figureheads were being very, very good boys.