git-sh-i18n.sh: add GIT_GETTEXT_POISON support

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>

git-sh-i18n.sh

@@ -5,6 +5,8 @@
 # This is a skeleton no-op implementation of gettext for Git. It'll be
 # replaced by something that uses gettext.sh in a future patch series.
 
+if test -z "$GIT_GETTEXT_POISON"
+then
 	gettext () {
 		printf "%s" "$1"
 	}
@@ -15,3 +17,13 @@ eval_gettext () {
 			git sh-i18n--envsubst "$1"
 		)
 	}
+else
+	gettext () {
+		printf "%s" "# GETTEXT POISON #"
+	}
+
+	eval_gettext () {
+		printf "%s" "# GETTEXT POISON #"
+	}
+fi
+