def postpone next_renewal_date, bulk=false
      return false unless link? :postpone
      reload follow_link(:postpone,
        :params => { :next_renewal_date => next_renewal_date, :bulk => bulk }
      )
      true
    end
def postpone next_renewal_date, bulk=false
      return false unless link? :postpone
      reload follow_link(:postpone,
        :params => { :next_renewal_date => next_renewal_date, :bulk => bulk }
      )
      true
    end
Postpone a subscription's renewal date.

 @return [true, false] +true+ when successful, +false+ when unable to
   (e.g., the subscription is not active).
 @param next_renewal_date [Time] when the subscription should renew.
 @param bulk [boolean] set to true for bulk updates (bypassing 60 second wait).