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/decomposePar.C

@@ -311,7 +311,7 @@ int main(int argc, char *argv[])
         wordHashSet names;
         forAllConstIters(rp, iter)
         {
-            names.insertMany(iter.object());
+            names.insert(iter.object());
         }
 
         regionNames = names.sortedToc();

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();