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)

applications/utilities/mesh/advanced/refinementLevel/refinementLevel.C

@@ -184,11 +184,7 @@ int main(int argc, char *argv[])
         const DynamicList<label>& bin = bins[binI];
 
         cellSet cells(mesh, "vol" + name(binI), bin.size());
-
-        forAll(bin, i)
-        {
-            cells.insert(bin[i]);
-        }
+        cells.insertMany(bin);
 
         Info<< "    " << lowerLimits[binI] << " .. " << upperLimits[binI]
             << "  : writing " << bin.size() << " cells to cellSet "