Speed up add to cart: Update the order once per fee calculation, rather than for every line item x fee

spec/models/spree/order_spec.rb

@@ -54,6 +54,8 @@ describe Spree::Order do
       product_distribution.should_receive(:create_adjustment_for).with(line_item)
       subject.stub(:product_distribution_for) { product_distribution }
 
+      subject.should_receive(:update!)
+
       subject.update_distribution_charge!
     end
 
@@ -65,6 +67,8 @@ describe Spree::Order do
 
       subject.stub(:product_distribution_for) { nil }
 
+      subject.should_receive(:update!)
+
       subject.update_distribution_charge!
     end
 
@@ -90,6 +94,8 @@ describe Spree::Order do
       OpenFoodNetwork::EnterpriseFeeCalculator.any_instance.stub(:create_order_adjustments_for)
       subject.stub(:order_cycle) { order_cycle }
 
+      subject.should_receive(:update!)
+
       subject.update_distribution_charge!
     end