ENH: improve separation of OpenFOAM and ThirdParty mpi-libraries

- drop FOAM_MPI_LIBBIN variable in favour of FOAM_MPI from which
  two different locations can be determined.

  Previously there was something like this:

      FOAM_MPI_LIBBIN = $FOAM_LIBBIN/openmpi-1.5.1

  We now instead determine the locations from the FOAM_MPI directly:

      FOAM_MPI=openmpi-1.5.1

          $FOAM_LIBBIN/$FOAM_MPI     -> OpenFOAM  mpi-related
          $FOAM_EXT_LIBBIN/$FOAM_MPI -> ThirdPary mpi-related

ENH: relocate ParaView libraries and plugins back under FOAM_LIBBIN

- as discussed with Mattijs

applications/utilities/postProcessing/graphics/PV3Readers/PV3FoamReader/vtkPV3Foam/Make/files

@@ -9,4 +9,4 @@ vtkPV3FoamMeshZone.C
 vtkPV3FoamUpdateInfo.C
 vtkPV3FoamUtils.C
 
-LIB = $(FOAM_EXT_LIBBIN)/libvtkPV3Foam
+LIB = $(FOAM_LIBBIN)/libvtkPV3Foam

applications/utilities/postProcessing/graphics/PV3Readers/PV3FoamReader/vtkPV3Foam/Make/options

@@ -19,5 +19,5 @@ LIB_LIBS = \
     -lfiniteVolume \
     -lgenericPatchFields \
     -llagrangian \
-    -L$(FOAM_EXT_LIBBIN) -lvtkPV3Readers \
+    -L$(FOAM_LIBBIN) -lvtkPV3Readers \
     $(GLIBS)

applications/utilities/postProcessing/graphics/PV3Readers/PV3blockMeshReader/vtkPV3blockMesh/Make/files

@@ -2,4 +2,4 @@ vtkPV3blockMesh.C
 vtkPV3blockMeshConvert.C
 vtkPV3blockMeshUtils.C
 
-LIB = $(FOAM_EXT_LIBBIN)/libvtkPV3blockMesh
+LIB = $(FOAM_LIBBIN)/libvtkPV3blockMesh

applications/utilities/postProcessing/graphics/PV3Readers/PV3blockMeshReader/vtkPV3blockMesh/Make/options

@@ -10,5 +10,5 @@ EXE_INC = \
 LIB_LIBS = \
     -lmeshTools \
     -lblockMesh \
-    -L$(FOAM_EXT_LIBBIN) -lvtkPV3Readers \
+    -L$(FOAM_LIBBIN) -lvtkPV3Readers \
     $(GLIBS)

applications/utilities/postProcessing/graphics/PV3Readers/vtkPV3Readers/Make/files

@@ -1,3 +1,3 @@
 vtkPV3Readers.C
 
-LIB = $(FOAM_EXT_LIBBIN)/libvtkPV3Readers
+LIB = $(FOAM_LIBBIN)/libvtkPV3Readers