checkout-index needs a working tree

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git.c

@@ -315,7 +315,8 @@ static void handle_internal_command(int argc, const char **argv)
 		{ "branch", cmd_branch, RUN_SETUP },
 		{ "bundle", cmd_bundle },
 		{ "cat-file", cmd_cat_file, RUN_SETUP },
-		{ "checkout-index", cmd_checkout_index, RUN_SETUP },
+		{ "checkout-index", cmd_checkout_index,
+			RUN_SETUP | NEED_WORK_TREE},
 		{ "check-ref-format", cmd_check_ref_format },
 		{ "check-attr", cmd_check_attr, RUN_SETUP | NEED_WORK_TREE },
 		{ "cherry", cmd_cherry, RUN_SETUP },