I recently learned that Johnnie A. Clark, Jr . had died in his sleep at 90 years of age. For longtime farmers market shoppers, you may recall the retired postman turned farmer, who held court on Saturday mornings among his offerings of cut carrots and greens. A real gentleman, Mr. Clark could also be fire and brimstone when issues of social justice and dignity for ordinary people are at stake. Unfortunately, Katrina ended his farmers market presence, but his legacy is worth emulating: He retired