Lost in one corner of a vast sepia-toned vista, a bearded farmer forks up a load of hay while a swirl of black crows circles overhead. It’s a lonely unbroken landscape. Lovers of the Caldecott Honor book “A Couple of Boys Have the Best Week Ever,” may well wonder if writer and illustrator Marla Frazee has entirely forsaken her antic sense of humor in “The Farmer and the Clown.” Not to worry.