Will Smith admits he can imagine cheating on his wife - but only with her permission.The Men In Black star said he and Jada Pinkett Smith agreed they would warn each other and ask for approval if they felt the need to sleep with someone else. 'Our perspective is, you don't avoid what's natural. You're going to be attracted to people,' said Smith, 36. 'In our marriage vows, we didn't say, "forsaking all others". The vow we made was that you will never hear I did something after the fact.' Eva Mendes, his co-star in his new movie Hitch, was...