The equity rally that saw the S&P 500 Index cap its third straight weekly advance — the best start since 1987 — is being driven by two things: Upward earnings revisions and the crush of money flowing into stocks. Optimism that the advance fueled by Donald Trump’s presidency will keep going is high among institutions and mom-and-pop investors alike. A survey by the University of Michigan shows that a record 66 percent of Americans believe the stock market will climb in the next year.