i18n: git-reset "Unstaged changes after reset" message

Gettextize the ""Unstaged changes after reset:" message. A test in
t7102-reset.sh explicitly checked for this message. Change it to skip
under GETTEXT_POISON=YesPlease.

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

builtin/reset.c

@@ -142,7 +142,7 @@ static int update_index_refresh(int fd, struct lock_file *index_lock, int flags)
 		return error(_("Could not read index"));
 
 	result = refresh_index(&the_index, (flags), NULL, NULL,
-			       "Unstaged changes after reset:") ? 1 : 0;
+			       _("Unstaged changes after reset:")) ? 1 : 0;
 	if (write_cache(fd, active_cache, active_nr) ||
 			commit_locked_index(index_lock))
 		return error ("Could not refresh index");

t/t7102-reset.sh

@@ -423,7 +423,7 @@ Unstaged changes after reset:
 M	file2
 EOF
 
-test_expect_success '--mixed refreshes the index' '
+test_expect_success C_LOCALE_OUTPUT '--mixed refreshes the index' '
 	echo 123 >> file2 &&
 	git reset --mixed HEAD > output &&
 	test_cmp expect output