Richard A. Posner was back at his old stomping grounds Wednesday.Wearing a suit and tie and bright blue running shoes, Posner appeared at the Dirksen Federal Courthouse four months after he abruptly retired from the 7th U.S. Circuit Court of Appeals.Posner left the bench after clashing with his fellow judges over what he contends is the 7th Circuit’s shabby treatment of pro se parties.He was back in the 7th Circuit’s courtroom — this time in the spectator section — to listen to arguments in cases …