ENH: fvMeshSubset improvements (issue #951)

- what was previously termed 'setLargeCellSubset()' is now simply
  'setCellSubset()' and supports memory efficient interfaces.

  The new parameter ordering avoids ambiguities caused by default
  parameters.

  Old parameter order:

      setLargeCellSubset
      (
          const labelList& region,
          const label currentRegion,
          const label patchID = -1,
          const bool syncCouples = true
      );

  New parameter order:

      setCellSubset
      (
          const label regioni,
          const labelUList& regions,
          const label patchID = -1,
          const bool syncCouples = true
      );

   And without ambiguity:

      setCellSubset
      (
          const labelUList& selectedCells,
          const label patchID = -1,
          const bool syncCouples = true
      );

- support bitSet directly for specifying the selectedCells for
  memory efficiency and ease of use.

- Additional constructors to perform setCellSubset() immediately,
  which simplifies coding.

  For example,

      meshParts.set
      (
          zonei,
          new fvMeshSubset(mesh, selectedCells)
      );

  Or even

      return autoPtr<fvMeshSubset>::New(mesh, selectedCells);

applications/solvers/incompressible/pimpleFoam/overPimpleDyMFoam/interpolatedFaces.H

@@ -25,10 +25,15 @@ labelList receptorNeigCell(mesh.nInternalFaces(), -1);
     PtrList<fvMeshSubset> meshParts(nZones);
     labelList nCellsPerZone(nZones, 0);
 
-    forAll(nCellsPerZone, zoneI)
+    // A mesh subset for each zone
+    forAll(meshParts, zonei)
     {
-        meshParts.set(zoneI, new fvMeshSubset(mesh));
-        meshParts[zoneI].setLargeCellSubset(zoneID, zoneI);
+        meshParts.set
+        (
+            zonei,
+            // Select cells where the zoneID == zonei
+            new fvMeshSubset(mesh, zonei, zoneID)
+        );
     }
 
     for (label faceI = 0; faceI < mesh.nInternalFaces(); faceI++)