to_xml needs to accept an options hash to conform with the expectations of Hash#to_xml

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@5362 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activeresource/lib/active_resource/base.rb

@@ -130,8 +130,8 @@ module ActiveResource
       connection.delete(self.class.element_path(id, prefix_options))
     end
 
-    def to_xml
-      attributes.to_xml(:root => self.class.element_name)
+    def to_xml(options={})
+      attributes.to_xml({:root => self.class.element_name}.merge(options))
     end
 
     # Reloads the attributes of this object from the remote web service.