ENH: consistency of HashSet setMany(), insertMany() with packed-list version

- this also provides a better separation of the intent
  (ie, inserting a single value, or inserting multiply values)

src/mesh/snappyHexMesh/meshRefinement/meshRefinement.C

@@ -1011,7 +1011,7 @@ Foam::label Foam::meshRefinement::splitFacesUndo
         {
             const labelList grownFaces(growFaceCellFace(errorFaces));
             errorFaces.clear();
-            errorFaces.insert(grownFaces);
+            errorFaces.insertMany(grownFaces);
         }