r12116: got rid of composite_trigger_done() and composite_trigger_error(), and

r12116: got rid of composite_trigger_done() and composite_trigger_error(), and
instead make the normal composite_done() and composite_error()
functions automatically trigger a delayed callback if the caller has
had no opportunity to setup a async callback

this removes one of the common mistakes in writing a composite function
(This used to be commit f9413ce792ded682e05134b66d433eeec293e6f1)