屏蔽滑动返回手势
self.navigationController.interactivePopGestureRecognizer.enabled = NO;
重新开启滑动返回手势
self.navigationController.interactivePopGestureRecognizer.enabled = YES;
系统级滑动返回手势的屏蔽和开启
原文：http://www.cnblogs.com/AliliWl/p/4917736.html
