The opening night party Thursday for the Broadway bow of “Good People” may have been at B.B. King’s in midtown Manhattan, but the subject of a lot of conversations was South Boston.That’s where playwright David Lindsay-Abaire (“Rabbit Hole”) grew up, and he funneled his memories of the place into a play that he said was “incredibly personal, but not all autobiographical.” The accent, of course, is a big deal. The cast, led by Frances McDormand, all worked hard on getting it right. You’d never know it, but Lindsay-Abaire used to have that accent too. When he went to private school at 11, the future scribe used to switch back and forth depending on whether he was at school or at home. “That’s just like being bilingual,” he said. It’s not just the accent that renders cast member Becky Ann Baker nearly unrecognizable on stage. It’s the painted-on eyebrows and the hair, which aud members assume is a really spectacular wig. Except it’s not. The most surprising news of the evening: “It’s my real hair!” she vowed.