LONDON — A pair of African distance runners took down what was once among the most unthinkable records in sports on Sunday, shattering the long-unapproachable two-hour barrier in the 26.2-mile (42.2-kilometer) marathon. Sabastian Sawe of Kenya won the London Marathon in 1 hour, 59 minutes and 30 seconds, bettering the previous men’s world record by an astonishing 65 seconds. He beat Ethiopia’s Yomif Kejelcha , who was running his first marathon and finished in 1:59.41. “What comes today is not