Don't show gitlink directories when we want "other" files

When "show_other_directories" is set, that implies that we are looking
for untracked files, which obviously means that we should ignore
directories that are marked as gitlinks in the index.

This fixes "git status" in a superproject, that would otherwise always
report that subprojects were "Untracked files:"

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/dir.c b/dir.c
index 7b91501..6564a92 100644
--- a/dir.c
+++ b/dir.c
@@ -375,6 +375,8 @@
 		return recurse_into_directory;
 
 	case index_gitdir:
+		if (dir->show_other_directories)
+			return ignore_directory;
 		return show_directory;
 
 	case index_nonexistent: