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: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

dir.c

@@ -375,6 +375,8 @@ static enum directory_treatment treat_directory(struct dir_struct *dir,
 		return recurse_into_directory;
 
 	case index_gitdir:
+		if (dir->show_other_directories)
+			return ignore_directory;
 		return show_directory;
 
 	case index_nonexistent: