See if we can improve the TryGetValueByReflection method when using dynamic objects.

A memory leak occurs when RadPropertyGrid instaces are loaded/unloaded multiple times. 

The issue manifests even more if the PropertyGrid contains fields for editing DateType types. 

 SelectedPropertyDefinitions are not cleared when RadPropertyGrid.Item being changed.

This issue has been reopen as the fix for it turned out to cause other problems.