Fix view context

Closes #313

lib/draper/system.rb

@@ -12,7 +12,9 @@ module Draper
     end
 
     def self.setup_action_mailer(component)
-      include Draper::ViewContext
+      component.class_eval do
+        include Draper::ViewContext
+      end
     end
   end
 end

lib/draper/view_context.rb

@@ -26,11 +26,6 @@ module Draper
 
     def self.build_view_context
       current_controller.view_context.tap do |context|
-        context.instance_eval do
-          def url_options
-            ActionMailer::Base.default_url_options
-          end
-        end unless context.request
         if defined?(ActionController::TestRequest)
           context.controller.request ||= ActionController::TestRequest.new
           context.request            ||= context.controller.request