This remote helper invokes external command and passes raw smart transport
stream through it. This is useful for instance for invoking ssh with
one-off odd options, connecting to git services in unix domain
sockets, in abstract namespace, using TLS or other secure protocols,
etc...
Signed-off-by: Ilari Liusvaara <ilari.liusvaara@elisanet.fi> Signed-off-by: Junio C Hamano <gitster@pobox.com>