Goodbye, summer. With Labor Day marking the unofficial end of summer, traders and portfolio managers will return from vacations and be back at their desks in full force. Portfolios tend to see some house-cleaning adjustments. Trading volumes pick up. Midterm elections are also on the horizon this year, which can add volatility in the run-up to November. This holiday-shortened week of trading gets started with a bang: a fresh batch of inflation data that will influence the Federal Reserve's next move on interest rates; an iPhone launch event that will double as an introduction to the new CEO of the…