United Airlines said Friday that it is raising its fees for checking bags, following a similar move earlier this week by American Airlines.Starting with tickets booked Saturday, economy-class passengers on domestic flights will be charged $5 more. That will bring the price to$35 if they pay online at least 24 hours before the flight, and $40 after that.The fee for a second checked bag will also rise$5, climbing to $45 in advance online and$50 at the airport.Passengers in premium cabins, holders of United ...