checkout: call the new submodule update test framework

Test that the checkout command updates the work tree as expected with
and without the '-f' flag.

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

t/t2013-checkout-submodule.sh

@@ -3,6 +3,7 @@
 test_description='checkout can handle submodules'
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-submodule-update.sh
 
 test_expect_success 'setup' '
 	mkdir submodule &&
@@ -62,4 +63,8 @@ test_expect_success '"checkout <submodule>" honors submodule.*.ignore from .git/
 	! test -s actual
 '
 
+test_submodule_switch "git checkout"
+
+test_submodule_forced_switch "git checkout -f"
+
 test_done