ISPN-263 Handle cluster partitions

https://issues.jboss.org/browse/ISPN-263
A good starting point is the documentation commit which describes the implemented functionality.
Most of the code is around playing with state transfer so dan's input is important :-)
2 or more nodes could disappear at the same time without forming a separate partition, like with the leap second bug. Better to say that we assume a split brain whenever numOwners or more nodes disappear.