Manually display nodes

Method to force display of nodes (main-thread affined). Added a sample project that will demonstrate how to manually display nodes. Removed the UIWindow layer pool hack.
hmm.  since `-__layout` and this new `-display` method are main-thread-affined and require a backing store, the automatic Core Animation-triggered layout and display passes can potentially already be running at this point.  alternatively, those passes might be triggered after an explicit `-display` call.  have we tested these scenarios?