Force iOS 6 app portrait only (add to a UIViewController subclass).

forcePortrait.m

/* in iOS 5
// Force app to be portrait-only
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
*/

// iOS 6 interface orientation support. Only rotate on iPad.
- (BOOL)shouldAutorotate {
    if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
        return YES;
    } else {
        return NO;
    }
}

// iOS 6 interface orientation support. Only rotate on iPad.
- (NSUInteger)supportedInterfaceOrientations {
    if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
        return UIInterfaceOrientationMaskAll;
    } else {
        return UIInterfaceOrientationMaskPortrait;
    }
}