Updating tintColor of presented popover

In order to change the tintColor of a currently presented popover I had to make a small change to your handy classe.

The change in action without dismissing the popover:
![img](http://f.cl.ly/items/39323611172F0m2B1k2D/Screen%20Recording%202014-11-06%20at%2011.42%20PM.gif)

There is still the need to manually relayout the popover.

Easy on iOS 8 with:
```objc
[myPresentedViewController.popoverPresentationController.containerView setNeedsLayout];
```
Ugly on iOS 7:
```objc
for (UIView *view in myPresentedViewController.view.superview.superview.subviews) {
    if ([view isKindOfClass:[DDPopoverBackgroundView class]]) {
        [view setNeedsLayout];
        [view layoutIfNeeded];
        break;
    }
}
```

Maybe you have a better idea to achieve this?