Add serialization_options

Prior to 0.9, @options was used to see the options passed to to_json. For some reason, with 0.9 the options were no longer passed and were entirely inaccessible within a Serializer.

This restores the access by placing it in an attribute named serializer_options.

lib/active_model/serializable.rb

@@ -9,11 +9,11 @@ module ActiveModel
     def as_json(options={})
       instrument('!serialize') do
         if root = options.fetch(:root, json_key)
-          hash = { root => serializable_object }
+          hash = { root => serializable_object(options) }
           hash.merge!(serializable_data)
           hash
         else
-          serializable_object
+          serializable_object(options)
         end
       end
     end

lib/active_model/serializer.rb

@@ -273,7 +273,10 @@ end
       end]
     end
 
+    attr_accessor :serialization_options
+
     def serializable_object(options={})
+      self.serialization_options = options
       return @wrap_in_array ? [] : nil if @object.nil?
       hash = attributes
       hash.merge! associations