globalMeshData: Changed the communicator for the reductions

Avoids problems with overlapping communicationbetween these reductions
and the calculation of deltaCoeffs.  This is a temporary fix while code
reorganizations are undertaken to ensure the globalMeshData is updated
before deltaCoeffs are requested.

Resolves bug-report http://www.openfoam.org/mantisbt/view.php?id=1780