Skip methods that distributor can't use in Package

This ensures that Spree's shipping methods take into account the ones
the order's distributor uses.

This reimplements what `#available_to_order_with_distributor_check?`
used to do and it doesn't work with Spree 2.0.4.

app/models/spree/shipping_method_decorator.rb

@@ -42,12 +42,6 @@ Spree::ShippingMethod.class_eval do
     ]
   end
 
-  def available_to_order_with_distributor_check?(order)
-    available_to_order_without_distributor_check?(order) &&
-      self.distributors.include?(order.distributor)
-  end
-  alias_method_chain :available_to_order?, :distributor_check
-
   def within_zone?(order)
     if order.ship_address
       zone && zone.include?(order.ship_address)

app/models/stock/package.rb

@@ -0,0 +1,33 @@
+# Extends Spree's Package implementation to skip shipping methods that are not
+# valid for OFN.
+#
+# It requires the following configuration in config/initializers/spree.rb:
+#
+#   Spree.config do |config|
+#     ...
+#     config.package_factory = Stock::Package
+#   end
+#
+module Stock
+  class Package < Spree::Stock::Package
+    # Skips the methods that are not used by the order's distributor
+    #
+    # @return [Array<Spree::ShippingMethod>]
+    def shipping_methods
+      super.delete_if do |shipping_method|
+        !ships_with?(order.distributor, shipping_method)
+      end
+    end
+
+    private
+
+    # Checks whether the given distributor provides the specified shipping method
+    #
+    # @param distributor [Spree::Enterprise]
+    # @param shipping_method [Spree::ShippingMethod]
+    # @return [Boolean]
+    def ships_with?(distributor, shipping_method)
+      distributor.shipping_methods.include?(shipping_method)
+    end
+  end
+end