django1.2中的消息框架有问题

我正在运行django1.2beta并尝试新特性:消息框架。

http://docs.djangoproject.com/en/dev/ref/contrib/messages/

messages 变量为空。我仔细检查了所有的设置,它们好像和手册上的一样。有什么问题吗?

设置.py

MIDDLEWARE_CLASSES = (
    'django.middleware.common.CommonMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware', #send messages to users
    'django.middleware.locale.LocaleMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',

    #debug tool
    'debug_toolbar.middleware.DebugToolbarMiddleware',
)

TEMPLATE_CONTEXT_PROCESSORS = (
    'django.contrib.messages.context_processors.messages', #send messages to users
    'django.core.context_processors.auth',
)

#Store messages in sessions
MESSAGE_STORAGE = 'django.contrib.messages.storage.session.SessionStorage';

INSTALLED_APPS = (
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    #'django.contrib.sites',
    'django.contrib.admin',
    'django.contrib.messages', 
    'debug_toolbar',

    #my apps
    #...
)

视图.py

def myview(request):

    from django.contrib import messages

    messages.error(request, 'error test');   
    messages.success(request, 'success test');   

    return render_to_response('mytemplate.html', locals()); 

{% for message in messages %}
        {{ message }}<br />
{% endfor %}

在模板中不输出任何内容。