Merge branch 'po/object-id'

* po/object-id: sha1_file: convert index_stream to struct object_id sha1_file: convert hash_sha1_file_literally to struct object_id sha1_file: convert index_fd to struct object_id sha1_file: convert index_path to struct object_id read-cache: convert to struct object_id builtin/hash-object: convert to struct object_id