Fixing product discard and classifications issue

When removing a product via discard, it was destroying all
classifications via delete_all, acts as list callbacks were
not called leaving gaps in position.

core/app/models/spree/product.rb

@@ -25,7 +25,7 @@ class Product < Spree::Base
  variants_including_master.discard_all
  self.product_option_types = []
  self.product_properties = []
- self.classifications = []
+ self.classifications.destroy_all
  self.product_promotion_rules = []
  end
 

core/spec/models/spree/classification_spec.rb

@@ -44,6 +44,18 @@ def positions_to_be_valid(taxon)
  end
  end
 
+ context "Discard'ing a product" do
+ before :each do
+ element = taxon_with_5_products.products[1]
+ expect(element.classifications.first.position).to eq(2)
+ element.discard
+ end
+
+ it "resets positions" do
+ expect positions_to_be_valid(taxon_with_5_products)
+ end
+ end
+
  context "replacing taxon's products" do
  before :each do
  products = taxon_with_5_products.products.to_a