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/functionObjects/field/turbulenceFields/turbulenceFields.C

@@ -146,7 +146,7 @@ bool Foam::functionObjects::turbulenceFields::read(const dictionary& dict)
     }
     else
     {
-        fieldSet_.insertMany(wordList(dict.lookup("fields")));
+        fieldSet_.insert(wordList(dict.lookup("fields")));
     }
 
     Info<< type() << " " << name() << ": ";