隐藏TabBar，真机有效

当push到下一级控制器时TabBar隐藏，当pop回控制器时显示

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        self.hidesBottomBarWhenPushed=YES;
    }
    return self;
}