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.

src/mesh/snappyHexMesh/meshRefinement/meshRefinement.C

@@ -1021,7 +1021,7 @@ Foam::label Foam::meshRefinement::splitFacesUndo
         {
             const labelList grownFaces(growFaceCellFace(errorFaces));
             errorFaces.clear();
-            errorFaces.insertMany(grownFaces);
+            errorFaces.insert(grownFaces);
         }