Conversion from uchar[20] to struct object_id continues.

* po/object-id:
  sha1_file: rename hash_sha1_file_literally
  sha1_file: convert write_loose_object to object_id
  sha1_file: convert force_object_loose to object_id
  sha1_file: convert write_sha1_file to object_id
  notes: convert write_notes_tree to object_id
  notes: convert combine_notes_* to object_id
  commit: convert commit_tree* to object_id
  match-trees: convert splice_tree to object_id
  cache: clear whole hash buffer with oidclr
  sha1_file: convert hash_sha1_file to object_id
  dir: convert struct sha1_stat to use object_id
  sha1_file: convert pretend_sha1_file to object_id