Moved director_write_manager_t<>::on_disconnect (which did nothing) to the .tcc file.
Added `sessions` to directory_write_manager_t, to prevent multiple initialization messages from being sent.
Added an editorial comment.
Added some largely redundant ASSERT_NO_CORO_WAITINGs.
Added comment in peers_list_callback_t.
Improved comment in peers_list_callback_t.
Changed directory_write_manager_t<metadata_t>::on_change to use spawn_sometime again.