transport-helper: update remote helper namespace

transport-helper: update remote helper namespace

When pushing, the remote namespace is updated correctly
(e.g. refs/origin/master), but not the remote helper's
(e.g. refs/testgit/origin/master), which currently is only
updated while fetching.

Since the remote namespace is used to tell fast-export which commits
to avoid (because they were already imported/exported), it makes
sense to have them in sync so they don't get generated twice. If the
remote helper was implemented properly, they would be ignored, if
not, they probably would end up repeated.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>