Created Issue: Selector.SelectedMemberPath no longer supports bool? properties [19524]

I recently upgraded from version 1.7.4644.13122 to 1.9.0.0 and it seems that I've been broken by a change of behavior in `Selector`. Previously, I was able to set `SelectedMemberPath` to a `Nullable<bool>` property and it worked fine. However, now the `GetSelectedMemberPathProperty` method checks whether the target property is `typeof(bool)`, which obviously fails.

Is there any reason for this regression? I've worked around it in my view models for now, but it would be nice to re-enable this scenario. If you're wondering why my property is `bool?`, I have a base `CheckableItemViewModel` that I extend with various subclasses. Some of those subclasses are used in scenarios where `null` is a valid value (ie. trees of check boxes) whilst others are not.

Thanks,
Kent