STYLE: use range-for when looping dictionary entries.

- as part of the cleanup of dictionary access methods (c6520033c9c4)
  made the dictionary class single inheritance from IDLList<entry>.

  This eliminates any ambiguities for iterators and allows
  for simple use of range-for looping.

  Eg,
      for (const entry& e : topDict))
      {
          Info<< "entry:" << e.keyword() << " is dict:" << e.isDict() << nl;
      }

   vs

      forAllConstIter(dictionary, topDict, iter))
      {
          Info<< "entry:" << iter().keyword()
              << " is dict:" << iter().isDict() << nl;
      }