submodule: fix quoting in relative_path()
Commit
caca2c1 (submodule: drop the top-level requirement) introduced a
relative_path helper but does not quote $curdir when it is stripped from
the front of a target path. In this particular case this should be safe
even with special characters because we only do this after checking that
$target begins with "$curdir/" which is quoted correctly, but we should
quote the variable to be certain that there is not some obscure case
where we this could strip more or less than we want.
Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>