patch for coupon create_discount method

	 def create_discount(order)
	    return if order.coupon_credits.reload.detect { |credit| credit.adjustment_source_id == self.id }
	    if eligible?(order) and amount = calculator.compute(order.line_items)
	      amount = order.item_total if amount > order.item_total
	      order.coupon_credits.reload.clear unless combine? and order.coupon_credits.all? { |credit| credit.adjustment_source.combine? }
	      order.save
	      coupon_credits.create({
	          :order => order,
	          #:amount => amount, #exclude this key / value to force recalculation 
	          :description => "#{I18n.t(:coupon)} (#{code})"
	        })
	    end