NAME
	CBD_POST -- Post availability of a clip to the clipboard.

   FUNCTION
	Indicate to the clipboard device that data is available for
	use by accessors of the clipboard.  This is intended to be
	used when a cut is large, in a private data format, and/or
	changing frequently, and it thus makes sense to avoid
	converting it to an IFF form and writing it to the clipboard
	unless another application wants it.  The post provides a
	message port to which the clipboard device will send a satisfy
	message if the data is required.

	If the satisfy message is received, the write associated with
	the post must be performed.  The act of writing the clip
	indicates that the message has been received: it may then be
	re-used by the clipboard device, and so must actually be
	removed from the satisfy message port so that the port is not
	corrupted.

	If the application wishes to determine if a post it has
	performed is still the current clip, it should check the
	post's io_ClipID with that returned by the CBD_CURRENTREADID
	command.  If the current read io_ClipID is greater, the clip
	is not still current.

	If an application has a pending post and wishes to determine
	if it should satisfy it (e.g. before it exits), it should
	check the post's io_ClipID with that returned by the
	CBD_CURRENTWRITEID command.  If the current write io_ClipID is
	greater, there is no need to satisfy the post.

   IO REQUEST
	io_Message	mn_ReplyPort set up
	io_Device	preset by OpenDevice
	io_Unit		preset by OpenDevice
	io_Command	CBD_POST
	io_Data		pointer to satisfy message port
	io_ClipID	zero

   RESULTS
	io_Error	non-zero if an error occurred
	io_ClipID	the clip ID assigned to this post, to be used
			in the write command if this is satisfied