interpret-trailers: allow running outside a repository

It may be useful to run git-interpret-trailers without needing to be in
a repository.

Signed-off-by: John Keeping <john@keeping.me.uk>
Acked-by: Christian Couder <christian.couder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git.c

@@ -417,7 +417,7 @@ static struct cmd_struct commands[] = {
 	{ "index-pack", cmd_index_pack, RUN_SETUP_GENTLY },
 	{ "init", cmd_init_db, NO_SETUP },
 	{ "init-db", cmd_init_db, NO_SETUP },
-	{ "interpret-trailers", cmd_interpret_trailers, RUN_SETUP },
+	{ "interpret-trailers", cmd_interpret_trailers, RUN_SETUP_GENTLY },
 	{ "log", cmd_log, RUN_SETUP },
 	{ "ls-files", cmd_ls_files, RUN_SETUP },
 	{ "ls-remote", cmd_ls_remote, RUN_SETUP_GENTLY },