transport-helper: add no-private-update capability
Since
664059fb (transport-helper: update remote helper namespace,
2013-04-17), a 'push' operation on a remote helper updates the
private ref by default. This is often a good thing, but it can also
be desirable to disable this update to force the next 'pull' to
re-import the pushed revisions.
Allow remote-helpers to disable the automatic update by introducing a new
capability.
Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>