Merge branch 'refs/heads/t/command_handler_cleanups'

Cooking for about two months.

* refs/heads/t/command_handler_cleanups: (39 commits)
  com_addatt(): Return negative on errors
  com_rm(): In force mode, don't complain if no paths matched.
  aft: Unify handling of hash and path duplicates.
  afs: Provide pbout para_buffer for each callback.
  afs: Make afs callbacks more flexible.
  afs: Rename callback_function to afs_callback.
  com_check(): Add attribute checking.
  Let afs_event() return int.
  playlist_check_callback(): Return negative on errors
  mood_check_callback(): Return negative on errors
  com_mvblob(): Return negative on errors
  com_addblob(): Return negative on errors
  com_rmblob(): Return negative on errors, cleanup
  com_catblob(): Return negative on errors
  com_lsblob(): Return negative on errors
  rmatt: Cleanup callback.
  com_rmatt(): Return negative on errors
  com_mvatt(): Return negative on errors
  com_lsatt(): Return negative on errors
  com_init(): Return negative on errors
  ...