Shuffle the playlist.  By default, this task is delegated to dr_unsort(1).
However, if draai runs in "sloppy" or in "native shuffle" mode, then mpc native
shuffling is done (by calling "mpc shuffle").  Draai runs in "sloppy" mode when
the DR_SLOPPY environment variable is set, or when the --sloppy option is
passed.  Draai runs in "native shuffle" mode when the DR_SHUFFLE_NATIVE
environment variable is set.