By Carol MorelloWashington Post Staff WriterSunday, June 20, 2010; A04 This is the scary season for the nation's census takers. Since they began making follow-up house calls in early May, census takers have encountered vitriol, menace and flashes of violence. They have been shot at with pellet guns and hit by baseball bats. They have been confronted with pickaxes, crossbows and hammers. They've…