STYLE: revert bitSet/HashSet setMany() to set() method (issue #837)

- improves backward compatibility and more naming consistency.
  Retain setMany(iter1, iter2) to avoid ambiguity with the
  PackedList::set(index, value) method.

applications/utilities/parallelProcessing/decomposePar/domainDecompositionMesh.C

@@ -451,7 +451,7 @@ void Foam::domainDecomposition::decomposeMesh()
             const labelList& facePoints = fcs[mag(facei) - 1];
 
             // Mark the face points as being used
-            pointsInUse.setMany(facePoints);
+            pointsInUse.set(facePoints);
         }
 
         procPointAddressing_[proci] = pointsInUse.sortedToc();