Add definitions needed for InitiateShutdown() to winreg.h

Source:
http://msdn.microsoft.com/en-us/library/windows/desktop/aa376872%28v=vs.85%29.aspx

Patch by Frank Fesevur <ffes at users.sourceforge.net>.
(cherry picked from commit e6afbb0406de4f912a07f4f33e45872decc9ee05)