add: refuse to add working tree items beyond symlinks

This is the same fix for the issue of adding "sym/path" when "sym" is a
symblic link that points at a directory "dir" with "path" in it.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/dir.c b/dir.c
index 29d1d5b..ae7046f 100644
--- a/dir.c
+++ b/dir.c
@@ -727,8 +727,12 @@
 
 int read_directory(struct dir_struct *dir, const char *path, const char *base, int baselen, const char **pathspec)
 {
-	struct path_simplify *simplify = create_simplify(pathspec);
+	struct path_simplify *simplify;
 
+	if (has_symlink_leading_path(strlen(path), path))
+		return dir->nr;
+
+	simplify = create_simplify(pathspec);
 	read_directory_recursive(dir, path, base, baselen, 0, simplify);
 	free_simplify(simplify);
 	qsort(dir->entries, dir->nr, sizeof(struct dir_entry *), cmp_name);