class Rufus::Scheduler::CronLine

level cron...
examining a whole, that can take more than seconds for a seconds
#brute_frequency, on the other hand, will compute the frequency by

cron line.
Returns a quickly computed approximation of the frequency for this

def frequency
  return brute_frequency unless @seconds && @seconds.length > 1
  delta = 60
  prev = @seconds[0]
  @seconds[1..-1].each do |sec|
    d = sec - prev
    delta = d if d < delta
  end
  delta
end