After 115 years of managing the Boston Marathon, the Boston Athletic Association has hit a wall. Too slow to adapt to the event’s evolution, the organizers face their greatest challenge since they commercialized the marathon 25 years ago: correct their flaws and catch up with the runaway growth of modern-day marathoning or risk degrading one of New England’s most revered institutions. Will the number of slots provided to fundraising charities be cut in the process?