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.
