read-tree: add t1013 for submodule updates

Test that the read-tree command updates the work tree as expected for
changes which don't result in conflicts with the '-m' and '--reset' flag.

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t1013-read-tree-submodule.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+test_description='read-tree can handle submodules'
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-submodule-update.sh
+
+test_submodule_switch "git read-tree -u -m"
+
+test_submodule_forced_switch "git read-tree -u --reset"
+
+test_done