implemented MPI processing within the main-branch files.

Note: this differs from the unify_dr branch which implements MPI
processing but in a new, unified framework for the different telescopes
tested and confirmed mpi-implementations of gmrt.py, lofar.py and aro.py.
added the 'normalize_counts' routine to aro.py
Merge pull request #12 from aberndsen/mpi3

MPI-enable