shift_log_age

# File lib/logger.rb, line 822
    def shift_log_age
      (@shift_age-3).downto(0) do |i|
        if FileTest.exist?("#{@filename}.#{i}")
          File.rename("#{@filename}.#{i}", "#{@filename}.#{i+1}")
        end
      end
      @dev.close rescue nil
      File.rename("#{@filename}", "#{@filename}.0")
      @dev = create_logfile(@filename)
      return true
    end