Check that display classmethod picks up validated_widget in request local

>>> import tw2.core as twc
>>> w = twc.Widget(id='w', template='genshi:tw2.core.test_templates.field_genshi', validator=twc.EmailValidator())
>>> w.validate({'w': 'fred'})
Traceback (most recent call last):
    ...
ValidationError: Must be a valid email address
>>> str(w.display())
'<p>fred Must be a valid email address</p>'
