push: --dry-run updates submodules when --recurse-submodules=on-demand

This patch adds a test to illustrate how push run with --dry-run doesn't
actually perform a dry-run when push is configured to push submodules
on-demand.  Instead all submodules which need to be pushed are actually
pushed to their remotes while any updates for the superproject are
performed as a dry-run.  This is a bug and not the intended behaviour of
a dry-run.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5531-deep-submodule-push.sh

@@ -427,7 +427,31 @@ test_expect_success 'push unpushable submodule recursively fails' '
 		cd submodule.git &&
 		git rev-parse master >../actual
 	) &&
+	test_when_finished git -C work reset --hard master^ &&
 	test_cmp expected actual
 '
 
+test_expect_failure 'push --dry-run does not recursively update submodules' '
+	(
+		cd work/gar/bage &&
+		git checkout master &&
+		git rev-parse master >../../../expected_submodule &&
+		> junk9 &&
+		git add junk9 &&
+		git commit -m "Ninth junk" &&
+
+		# Go up to 'work' directory
+		cd ../.. &&
+		git checkout master &&
+		git rev-parse master >../expected_pub &&
+		git add gar/bage &&
+		git commit -m "Ninth commit for gar/bage" &&
+		git push --dry-run --recurse-submodules=on-demand ../pub.git master
+	) &&
+	git -C submodule.git rev-parse master >actual_submodule &&
+	git -C pub.git rev-parse master >actual_pub &&
+	test_cmp expected_pub actual_pub &&
+	test_cmp expected_submodule actual_submodule
+'
+
 test_done