OSSystemSupport does not reflect VM / OS diversity

Hi,

while working on the OSTimeZone package I noticed that one Windows API
call requires Windows XP / Server 2003. Unfortunately, OSSystemSupport
and subclasses have not been update for quite a while, so the most
concrete class is still WinNTSystemSupport.
Now there are quite a lot of versions of Windows and a myriad Unix'es
around, but I think it's reasonable to add specific classes for the
following OSes:

- Windows XP
- Windows Server 2003
- Windows CE

Regards,
Holger