allow_unkown=True doesn't work with sections

[Antoine Millet]

I got the following error:

Traceback (most recent call last):
  File "test3.py", line 108, in <module>
    pconfig = config.parse()
  File "/home/antoine/Devel/dotconf/dotconf/__init__.py", line 28, in parse
    config = self._schema.validate(config)
  File "/home/antoine/Devel/dotconf/dotconf/schema/containers.py", line 403, in validate
    validated_section.register(child, name=name)
  File "/home/antoine/Devel/dotconf/dotconf/tree.py", line 106, in register
    raise TypeError('Child must be a ConfigValue or ConfigSection object')
TypeError: Child must be a ConfigValue or ConfigSection object

Seem because ConfigSection.iteritems() returns a list of section instead of expanding it.

[Antoine Millet]

Duplicate of #6