- add_person, remove_person, add_node, remove_node: fix case when person/node   is already part of/no longer a part of the slice
- add_person, remove_person, add_node, remove_node: fix case when person/node
  is already part of/no longer a part of the slice


dreibh/planetlab-lxc-plcapi,dreibh/planetlab-lxc-plcapi,dreibh/planetlab-lxc-plcapi,dreibh/planetlab-lxc-plcapi