af_snote sets the given text (in buf) as change note
of the specified ASO. Text must be null terminated.
af_snote requires a lock (see af_lock(3)) set on the specified ASO.
Af_rnote returns a pointer to the note attribute of the specified
ASO. The note text is returned in memory allocated by malloc(3).
Use free(3) to make the space available for further allocation.