cwTextBox Selection Range Improvements
Added BeforeSelChange and SelChanged events
Added private SetSelection method
	This method should always be used to change a selection range or caret position so that appropriate events will be raised
Added private NormalizeSelectionIndexes method
	keeps SelStart/Length within range of text
Added private SelectionWillChange method
	Returns true if passed new sel start/length/reverse direction will change the current selection
	This allows for short-circuiting in SetSelection
Refactored code that changes selection/caret position to use SetSelection method