Two prominent law enforcers in the U.S. who have been pushing Apple to do more to combat iPhone theft say they appreciate a new feature previewed earlier Monday that could help make stolen iPhones more difficult for thieves to resell.Related StoriesOpinion: Forget the keynote. WWDC is still about the developersApple's WWDC 2013 keynote in picturesApple makes full WWDC 2013 keynote video availab