git-submodule.sh: avoid "test <cond> -a/-o <cond>"

The construct is error-prone; "test" being built-in in most modern
shells, the reason to avoid "test <cond> && test <cond>" spawning
one extra process by using a single "test <cond> -a <cond>" no
longer exists.

Signed-off-by: Elia Pinto <gitter.spiros@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
git-submodule.sh: avoid "echo" path-like values

SysV-derived implementation of "echo" interprets some backslash
sequences as special instruction, e.g. "echo 'ab\c'" shows an
incomplete line with 'a' and 'b' on it.  Avoid using it when showing
a path-like values in the script.

Signed-off-by: Junio C Hamano <gitster@pobox.com>