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 :-)
this is not handled atm, it should be though. I don't think we should ever allow a merge *unless* the two partitions are in degraded mode and converge to an parent cluster. wdyt?