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/mesh/conversion/writeMeshObj/writeMeshObj.C

@@ -344,7 +344,7 @@ void writePointCells
     {
         const labelList& cEdges = mesh.cellEdges()[pCells[i]];
 
-        allEdges.insertMany(cEdges);
+        allEdges.insert(cEdges);
     }