From Yahoo! News: JERUSALEM (Reuters) – The United States and Israel have postponed an upcoming joint military exercise until later in the year, but sources in both countries denied on Sunday that the move was taken to avoid further escalating tensions with Iran. The air-defense drill, named "Austere Challenge 12," is expected to be the largest exercise between the two allies, who regularly hold joint military maneuvers. The Pentagon said it was scheduled for the spring, but now would