Pixels per inch will jump to an average of 200 in the second quarter of 2012.(Credit: DisplaySearch)iPhone 4S' retina display.Apple's next-gen iPad won't be the only new tablet design with lots more pixels. Market researcher DisplaySearch said today that the average pixel density of tablets will surge next year.The forecast calls for the average resolution of tablet displays to grow to more than 200 pixels per inch (PPI) in the second quarter of...