Airline passengers are getting grumpier, and it’s little wonder. Airlines keep shrinking the size of seats to stuff more people onto planes, those empty middle seats that once provided a little more room are now occupied and more people with tickets are being turned away because flights are overbooked. Private researchers who analyzed federal data on airline performance also said in a report being released Monday that consumer complaints to the Department of Transportation surged by one-fifth last year even though other measures such as on-time arrivals and mishandled baggage show airlines are doing a better job. …