rebase -i continue: don't skip commits that only change submodules

When git-rebase--interactive stops due to a conflict and the only change
to be committed is in a submodule, the test for whether there is
anything to be committed ignores the staged submodule change.  This
leads rebase to skip creating the commit for the change.

While unstaged submodule changes should be ignored to avoid needing to
update submodules during a rebase, it is safe to remove the
--ignore-submodules option to diff-index because --cached ensures that
it is only checking the index.  This was discussed in [1] and a test is
included to ensure that unstaged changes are still ignored correctly.

[1] http://thread.gmane.org/gmane.comp.version-control.git/188713

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase--interactive.sh

@@ -672,7 +672,7 @@ rearrange_squash () {
 case "$action" in
 continue)
 	# do we have anything to commit?
-	if git diff-index --cached --quiet --ignore-submodules HEAD --
+	if git diff-index --cached --quiet HEAD --
 	then
 		: Nothing to commit -- skip this
 	else

t/t3404-rebase-interactive.sh

@@ -624,8 +624,38 @@ test_expect_success 'submodule rebase -i' '
 	FAKE_LINES="1 squash 2 3" git rebase -i A
 '
 
+test_expect_success 'submodule conflict setup' '
+	git tag submodule-base &&
+	git checkout HEAD^ &&
+	(
+		cd sub && git checkout HEAD^ && echo 4 >elif &&
+		git add elif && git commit -m "submodule conflict"
+	) &&
+	git add sub &&
+	test_tick &&
+	git commit -m "Conflict in submodule" &&
+	git tag submodule-topic
+'
+
+test_expect_success 'rebase -i continue with only submodule staged' '
+	test_must_fail git rebase -i submodule-base &&
+	git add sub &&
+	git rebase --continue &&
+	test $(git rev-parse submodule-base) != $(git rev-parse HEAD)
+'
+
+test_expect_success 'rebase -i continue with unstaged submodule' '
+	git checkout submodule-topic &&
+	git reset --hard &&
+	test_must_fail git rebase -i submodule-base &&
+	git reset &&
+	git rebase --continue &&
+	test $(git rev-parse submodule-base) = $(git rev-parse HEAD)
+'
+
 test_expect_success 'avoid unnecessary reset' '
 	git checkout master &&
+	git reset --hard &&
 	test-chmtime =123456789 file3 &&
 	git update-index --refresh &&
 	HEAD=$(git rev-parse HEAD) &&