Change git-sh-i18n.sh to support the GIT_GETTEXT_POISON environment
variable like gettext.c does, this ensures that tests that use
git-sh-i18n.sh will fail under GETTEXT_POISON=YesPlease if they rely
on Git's C locale messages without declaring that they do.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>