As current ABC sitcoms go, Modern Family may own Halloween, but The Middle has just as firm a hold on Thanksgiving. This Midwestern family has grown a lot over the years – the kids, physically as well as emotionally – and gathering them around the holiday table has both measured and showcased those annual growth spurts. And then, of course, there are the visiting relatives… Except this year, the Hecks are the visitors, taking a holiday road trip to visit Frankie’s sister for Thanksgiving, a voyage destined to have its share of detours. Welcome to an annual TV event that, like “Treehouse of Horror” on The Simpsons, is marked by titles with Roman numerals. Yes, tonight on The Middle, it’s “Thanksgiving IX.”