"Bending the Arc" (Credit: Impact Partners) There’s something a little mind-bending about the idea that a documentary about global health could be one of the most life-affirming, optimistic films you might see this year. But that’s the case, because “Bending the Arc,” which opens this weekend, zeros in on the successes of three incredible friends, Paul Farmer, Jim Yong Kim and Ophelia Dahl, who helped flip the script on global health issues by getting effective treatments for people in Haiti and other countries with TB, AIDS and other conditions that might be in check in developed nations but not in the rest of the world. The three Harvard medical students used their expertise, optimism, determination — and mostly other people’s money — to shake the scientific community as well as a lethargic global health industry into treating people who had been written off as incapable of being helped.