Wire up the git-subtree(1) command, which is part of "contrib/". Note
that we have to move around the exact location where we include the
"contrib/" subdirectory so that it comes after building the docs so that
we have access to some of the common functionality.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
