Discards changes since the last IEditableObject.BeginEdit call.
This method is typically used to capture the IEditableObject.CancelEdit semantics of a System.Data.DataRowView.
This method will be ignored if called on an object that is not being edited.
If the owning list implements System.ComponentModel.IBindingList, calling IEditableObject.CancelEdit on an object created using IBindingList.AddNew discards the object.