ENH: enable MPI library variants (#1153)

- in addition to managing different vendors and versions, it may also
  be necessary or desirable to have a particular variant
  (eg, profiling, release, etc).

  Devise a new meaningful name for the variant and create a
  corresponding wmake rule.

  Eg, SYSTEMOPENMPI-profiling with a corresponding
      "wmake/rules/linux64Gcc/mplibSYSTEMOPENMPI-profiling" file
  that has suitable content for your system.

CONFIG: intel-mpi use intel64/ paths only for config and wmake rules (#1153)

- previously adjusted the config files, but missed the changes
  required for the wmake rules too.

  Now simply migrate to using  "intel64/{include,bin,lib}"
  instead of the older naming  "{include,bin,lib}64"

  These changes work since at least intel-mpi 2015 (5.x), but possibly
  earlier as well

wmake/rules/linux64Gcc/mplibINTELMPI

@@ -1,3 +1,3 @@
 PFLAGS     = -DMPICH_SKIP_MPICXX
-PINC       = -isystem $(MPI_ARCH_PATH)/include64
-PLIBS      = -L$(MPI_ARCH_PATH)/lib64 -lmpi
+PINC       = -isystem $(MPI_ARCH_PATH)/intel64/include
+PLIBS      = -L$(MPI_ARCH_PATH)/intel64/lib -lmpi