iOS 6的orientation还是比较奇葩的。我一开始以为只要把之前的- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation 改成 - (BOOL)shouldAutorotate和- (NSUInteger)supportedInterfaceOrientations的组合就行了，但是套了一层UINavigationController之后情况又变了：无论child view controller支持哪些orientation，UINavigationController总是会支持UIInterfaceOrientationMaskAllButUpsideDown。所以要让UINavigationController中的某些viewController通过自身的supportedInterfaceOrientations设置来调整orientation变得不可能。

最后在stackoverflow上面看到一个解决办法，看起来也是比较山寨的，但至少解决了问题：

@implementation UINavigationController (Rotation_IOS6)

-(BOOL)shouldAutorotate
{
    return [[self.viewControllers lastObject] shouldAutorotate];
}

-(NSUInteger)supportedInterfaceOrientations
{
    return [[self.viewControllers lastObject] supportedInterfaceOrientations];
}

- (UIInterfaceOrientation)preferredInterfaceOrientationForPresentation
{
    return [[self.viewControllers lastObject] preferredInterfaceOrientationForPresentation];
}

@end