This is implemented for now by calling fetch_objects(). It fetches
from all the promisor remotes.
Helped-by: Ramsay Jones <ramsay@ramsayjones.plus.com> Helped-by: Derrick Stolee <stolee@gmail.com> Signed-off-by: Christian Couder <chriscool@tuxfamily.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>