Add KERNEL32.SetThreadUILanguage() stub

[Thomas Weidenmueller]

Andreas Mohr wrote:
> Hello all,
> 
> this one is needed by XP's ping.exe and a reworked ReactOS version.
> 
> Andreas Mohr

This prototype is outdated. MS has documented this function in the
meanwhile:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/intl/mui_set_thread_ui_lang.asp

Best Regards,
Thomas Weidenmueller