Ordinarily, the talents of playwright and fiction writer are mutually exclusive. Rare it is that a writer shows a gift for both, though there are exceptions: Chekov, of course, was a genius who juggled drama and fiction effortlessly, and Oscar Wilde’s novella “The Picture of Dorian Gray” stacks up well against his numerous plays. Add to this list John Steinbeck, who adapted his own novel, “Of Mice and Men,” into a very effective drama in 1937, the same year of the book’s publication. Its simple, tragic material is a perfect fit for theater, and in many ways the drama is more powerful than its fiction counterpart.