rewind_offset

https://github.com/cmus/cmus/issues/22

rewind_offset (5) [-1-9999]
  If the position of the current track is smaller than rewind_offset,
  player_prev jumps to the previous track. Otherwise, player_prev jumps
  to the beginning of the current track. If rewind_offset=-1, player_prev
  always jumps to the previous track.