In particular, git-fast-import and -export link to each
other, and gitremote-helpers links to existing remote
helpers, and vice versa. Also link to fast-import from the
remote helper spec, as this is relevant for remote helpers
using the fast-import format.
Signed-off-by: Max Horn <max@quendi.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>