Makes dictionaries expandable when dealing with plists.

def _AtNonLeaf(self, attr_value, path):
    """Makes dictionaries expandable when dealing with plists."""
    if isinstance(attr_value, dict):
      for value in self.Expand(attr_value, path[1:]):
        yield value
    else:
      for v in objectfilter.ValueExpander._AtNonLeaf(self, attr_value, path):
        yield v