Specify class name for calculator association in calculated_adjustment

Otherwise, top-level classes that include this module will have an association that looks for ::Calculator, rather than Spree::Calculator

core/lib/spree/core/calculated_adjustments.rb

@@ -3,7 +3,7 @@ module Core
  module CalculatedAdjustments
  def self.included(klass)
  klass.class_eval do
- has_one :calculator, :as => :calculable, :dependent => :destroy
+ has_one :calculator, :class_name => "Spree::Calculator", :as => :calculable, :dependent => :destroy
  accepts_nested_attributes_for :calculator
  attr_accessible :calculator_type, :calculator_attributes
  validates :calculator, :presence => true