It’s another world premiere performance in Chicago. Playwright Douglas Post’s work “Shaw vs. Tunney,” directed by Nick Sandys and produced by Chicago attorney Charles Grippo, is playing through July 8 at Theater Wit, 1229 W. Belmont Ave.The play is based on “The Prizefighter and the Playwright,” a book by Chicagoan Jay R. Tunney, the son of world heavyweight-boxing champion Gene Tunney. It tells the story of an unusual relationship that developed between his father and George Bernard Shaw, a famous philosopher and …