i18n: git-merge "Wonderful" message

Gettextize the "Wonderful" message. A test in t7600-merge.sh
explicitly checked for this message. Change it to skip under
GETTEXT_POISON=YesPlease.
Signed-off-by: NÆvar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/merge.c

@@ -803,7 +803,7 @@ static int merge_trivial(void)
 	struct commit_list *parent = xmalloc(sizeof(*parent));
 
 	write_tree_trivial(result_tree);
-	printf("Wonderful.\n");
+	printf(_("Wonderful.\n"));
 	parent->item = lookup_commit(head);
 	parent->next = xmalloc(sizeof(*parent->next));
 	parent->next->item = remoteheads->item;

t/t7600-merge.sh

@@ -495,7 +495,7 @@ test_expect_success 'merge fast-forward in a dirty tree' '
 
 test_debug 'git log --graph --decorate --oneline --all'
 
-test_expect_success 'in-index merge' '
+test_expect_success C_LOCALE_OUTPUT 'in-index merge' '
 	git reset --hard c0 &&
 	git merge --no-ff -s resolve c1 >out &&
 	grep "Wonderful." out &&