i18n: git-merge "You have not concluded your merge" messages

Gettextize the "You have not concluded your merge messages. A test in
t3030-merge-recursive.sh explicitly checked for this message. Change
it to skip the test under GETTEXT_POISON=YesPlease.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3030-merge-recursive.sh

@@ -312,7 +312,7 @@ test_expect_success 'merge-recursive result' '
 
 '
 
-test_expect_success 'fail if the index has unresolved entries' '
+test_expect_success C_LOCALE_OUTPUT 'fail if the index has unresolved entries' '
 
 	rm -fr [abcd] &&
 	git checkout -f "$c1" &&