When a data context changes, it should be notified to all descendant controls who inherit the data context. This allows the `SelectingItemsControl` to defer setting the selected item until the `DataContext` has changed for the whole tree.
Renamed `OnDataContextChanging`/`OnDataContextChanged` to `OnDataContextBeginUpdate`/`OnDataContextEndUpdate` because `DataContextChanged` is now called from the property changed notification.
Fixes#507.
- Set `InheritanceParent` before Parent so that control doesn't
initially inherit the wrong DataContext
- Don't set `InheritanceParent` when setting `Parent` if
`InheritanceParent` already set
- Added `IDataTemplate.SupportsRecycling`
If a `ContentPresenter`s content is assigned a value which matches the
current `DataTemplate` then just change the
`ContentPresenter.DataContext` and the existing item will update itself.
Also made a few other changes along the way:
- Add MaxClientSize to ILayoutRoot
- Store IRenderRoot in Visual and use that to calculate
IsAttachedToVisualTree
- Make Affects* methods take multiple properties
Steven Kirk
Nikita Tsukanov
Steven Kirk