polymorphic deletion through a base pointer should not be allowed -> protected destructor (http://www.gotw.ca/publications/mill18.htm)

IndexRearrangementForStreams needs only a small subset of the Communicator's functionalities.
This change also makes testing easier. There is no need to derive from the concrete class Communicator to test IndexRearrangementForStreams anymore.

If the numberOfSendIndices is zero no entry should be added to the vector of sendProcessNeighbors. This commit fixes an error in MPI communication for some apps with grid refinement.

fix linker problems

Some variables were not assigned values in the constructor.  This caused an "MPI_ERR_COMM: invalid communicator" error when using multiple gpus.