MARCO AQUINO PERU’S Pedro Castillo has come a long way to be on the cusp of winning the Andean nation's presidential election. The son of peasant farmers, who lives humbly as a teacher in Peru's north and tends animals on his land, is the narrow favorite ahead of Sunday's run-off vote that has become a referendum on wealth and poverty in the copper-rich country. Castillo, 51, who represents the socialist Peru Libre party, shot to prominence in April when he shocked analysts and pollsters to win the first-round vote. He even caught some major news outlets off guard, as they…