A user-defined callback is called when the refcount drops to 0.
Reference counting is manually coded for several classes deriving from
PipeItem, so this change will help to share this code, and allow to remove
some ref/unref virtual functions in some interfaces when we can assume
every instance derives from this base class.
Signed-off-by: Christophe Fergeau <cfergeau@redhat.com>
Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
Reviewed-by: Jonathon Jongsma <jjongsma@redhat.com>
