Attempt to fix DependencyProperty notifications

Certain uses of WhenAny seem to not produce notifications, they all have the same
two properties when they don't work:

* It's reaching into an object (i.e. x => x.Foo.Bar.Baz)
* The root object is a DependencyObject

In a blind attempt to fix this, use the WPF way to generate notifications
instead of the SL Attached Property way.
Version bump to 4.3.1