Wrong parsing of MultiGeometry when containing nested MultiGeometry

[reverse-engineer]

When parsing e.g. https://developers.google.com/kml/documentation/us_states.kml, there is a bug because you do not allow a MultiGeometry (which you consider a Geometry) to contain another MultiGeometry. The nested MultiGeometry in the US state placeholders of above .kml file are thus ignored. Easy to fix I suspect by adding element.findall('%sMultiGeometry' % self.ns) line in the _get_multigeometry method.