winreg: Add MAX_SHUTDOWN_TIMEOUT define

Add define for MAX_SHUTDOWN_TIMEOUT as described in the WINE (1.7.1) version of winreg.h. This define is required for function(s) like InitiateSystemShutdown() as defined on MSDN (http://msdn.microsoft.com/en-us/library/windows/desktop/aa376873%28v=vs.85%29.aspx/html).