Christopher Stevens, a 52-year-old U.S. Ambassador to Libya who was killed on Tuesday during an attack on the U.S. Consulate in Benghazi, Libya, was born in Grass Valley in 1960. He was the son of Jan Stevens, who graduated from Grass Valley High School in 1951, and went on to work in the California Attorney General’s Office, said 78-year-old Grass Valley resident Lois Robinson, who was a classmate of Jan Stevens at the Nevada County high school in the 1950s. Christopher Stevens’ grandfather Elmer Stevens was a teacher at Grass Valley High School, before it consolidated with Nevada City High …