NAME
	CBD_CHANGEHOOK -- Add or remove a clip change hook

   FUNCTION
	CBD_CHANGEHOOK allows specification of a hook to be called
	when the data on the clipboard has changed.

   IO REQUEST
	io_Message	mn_ReplyPort set up
	io_Device	preset by OpenDevice
	io_Unit		preset by OpenDevice
	io_Command	CBD_CHANGEHOOK
	io_Length -     0 to remove, 1 to install this hook
	io_Data -       struct Hook *, the clip change hook

   HOOK ENVIRONMENT
       hook message - a ClipHookMsg, as defined in devices/clipboard.h
           chm_Type - 0, indicating that the message has the
               following fields:
           chm_ClipID - the clip ID of the clip triggering the change
       hook object - io_Unit