TreeView notifications fix

[John K. Hohm]

> Well, WinAmp seems to use CreateWindowExW to create the window, but I
> can't find where the window class is registered, it doesn't seem to
> appear in a +class trace anywhere. The string name is "#32770", so maybe
> it's internal.

Indeed, here is a list of system classes:

Class      Description 
---------- --------------------------------------------------------------
ComboLBox  The class for the list box contained in a combo box. 
DDEMLEvent Windows NT/Windows 2000/Windows XP: The class for Dynamic Data
           Exchange Management Library (DDEML) events. 
Message    Windows 2000/Windows XP: The class for a message-only window. 
#32768     The class for a menu. 
#32769     The class for the desktop window. 
#32770     The class for a dialog box. 
#32771     The class for the task switch window. 
#32772     Windows NT/Windows 2000/Windows XP: The class for icon titles.