TomTom International has updated its series of turn-by-turn navigation apps to take advantage of the new multitasking features in iOS 4. A required update for iOS 4 users, TomTom 1.4 adds support for the new background location feature available on multitasking-capable iOS 4 devices. The update provides continuous visual driving instructions on iPhone 4 and iPhone 3GS devices even while the user is on a call and background navigation for iPhone 4,…