t7401: make indentation consistent

Only leading whitespace is changed in this patch.

Signed-off-by: John Keeping <john@keeping.me.uk>
fix message in submodule
submodule: drop the top-level requirement

Use the new rev-parse --prefix option to process all paths given to the
submodule command, dropping the requirement that it be run from the
top-level of the repository.

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>