def buffer_prev
      buffer_update_info
      if @_buffer_ctr < 1
        buffer_last
        return
      end
      @_buffer_ctr -= 1 if @_buffer_ctr > 0
      x = @_buffer_ctr
      l = @_buffers[x]
      if l
        populate_buffer_from_filename x
        l = @_buffers[x]
        $log.debug "bp calling set_content with #{l.class} "
        set_content l, @_buffers_conf[x]
        buffer_update_position
      end
    end
def buffer_prev
      buffer_update_info
      if @_buffer_ctr < 1
        buffer_last
        return
      end
      @_buffer_ctr -= 1 if @_buffer_ctr > 0
      x = @_buffer_ctr
      l = @_buffers[x]
      if l
        populate_buffer_from_filename x
        l = @_buffers[x]
        $log.debug "bp calling set_content with #{l.class} "
        set_content l, @_buffers_conf[x]
        buffer_update_position
      end
    end
display previous buffer if any