The Walking Dead spent an entire season trapped on one farm because AMC cut the budget of its own biggest hit. Season 1 was the network's biggest ratings success ever. AMC's response was to slash season 2 from $3.4 million per episode to $2.75 million, while pocketing the Georgia tax credit, an effective 25% cut. Fewer locations, fewer zombies, fewer action scenes. So the writers parked the entire cast at Hershel's farm for a year. Frank Darabont, the Shawshank Redemption director who built…