add -p: do not attempt to coalesce mode changes

In 0392513f (add-interactive: refactor mode hunk handling, 2009-04-16),
we merged the interaction loops for mode changes and hunk staging.
This was fine at the time, because 0beee4c6 (git-add--interactive:
remove hunk coalescing, 2008-07-02) removed hunk coalescing.

However, in 7a26e653 (Revert "git-add--interactive: remove hunk
coalescing", 2009-05-16), we resurrected it.  Since then, the code
would attempt in vain to merge mode changes with diff hunks,
corrupting both in the process.

We add a check to the coalescing loop to ensure it only looks at diff
hunks, thus skipping mode changes.
Noticed-by: NKirill Smelkov <kirr@mns.spb.ru>
Signed-off-by: NThomas Rast <trast@student.ethz.ch>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-add--interactive.perl

@@ -841,6 +841,10 @@ sub coalesce_overlapping_hunks {
 	my ($last_o_ctx, $last_was_dirty);
 
 	for (grep { $_->{USE} } @in) {
+		if ($_->{TYPE} ne 'hunk') {
+			push @out, $_;
+			next;
+		}
 		my $text = $_->{TEXT};
 		my ($o_ofs) = parse_hunk_header($text->[0]);
 		if (defined $last_o_ctx &&

t/t3701-add-interactive.sh

@@ -164,7 +164,7 @@ test_expect_success FILEMODE 'stage mode but not hunk' '
 '
 
 
-test_expect_failure FILEMODE 'stage mode and hunk' '
+test_expect_success FILEMODE 'stage mode and hunk' '
 	git reset --hard &&
 	echo content >>file &&
 	chmod +x file &&