If he wins the Oscar for adapted screenplay for “Fences,” the late playwright August Wilson will join an impressive group of posthumous winners and nominees. Wilson won a Tony Award and a Pulitzer Prize for his 1983 play, which he later adapted into a screenplay. But it took more than 20 years for the movie version of “Fences” to come out; Wilson’s death at age 60 in October 2005 was well before t