Call RmShutdown() with proper action flags

[1] states that the "lActionFlags" parameter has to be "One or more
RM_SHUTDOWN_TYPE options" that "can be combined by an OR operator". Thus,
passing 0 is invalid, valid options are combinations of "RmForceShutdown"
and "RmShutdownOnlyRegistered".

Only use "RmShutdownOnlyRegistered" here for now as there should be a
separate user confirmation to force the shutdown of applications that do
not support being restarted by calling RegisterApplicationRestart().

[1]
http://msdn.microsoft.com/en-us/library/windows/desktop/aa373667%28v=vs.85%29.aspx