Redoing change done by commit 65e22b75 using the newer variables. This
addresses the Python2.6 issue with MPI4PY.

    Undefined symbols for architecture x86_64:
      "__PyByteArray_empty_string", referenced from:
      _PyMPI_Allocate in MPI.c.o

Change-Id: I1f1534887407c936a8c8e924e7248c98f6823f99