Rework XML import: * handle root and object node separately * prepare for other node classes * root nodes are only allowed at the very top of the XML hierarchy * there should be a single root node
Rework XML import:
* handle root and object node separately
* prepare for other node classes
* root nodes are only allowed at the very top of the XML hierarchy
* there should be a single root node

git-svn-id: 14be032f8f42541b1a281b51ae8ea69814daf20e@1680 4b44e086-7f34-40ce-a3bd-00e031736276

BlueBrain/hwloc,BlueBrain/hwloc,BlueBrain/hwloc,BlueBrain/hwloc