as this enum is not really usable yet (as MySQL server supports only one
shutdown level), and as SHUTDOWN_DEFAULT is still left to 0, this change
should disturb no user. Later (in 4.1.4 or 4.1.5) code will be pushed to
implement graceful shutdown using this enum.
mysqld >=4.1.3 will however understand shutdown requests sent by clients <4.1.3.
And mysqld <4.1.3 will understand shutdown requests sent by clients >=4.1.3
(it will ignore the level). Those shutdown level are just PLACEHOLDERS now.
So this change is just to make the 4.1 API suitable before it is frozen. Later
we will actually implement the shutdown levels.
