code: public int countLinks()
      {
          int count = 0;
          Link look = _dummyHead.getNextLogicalLink();
          while (look != null && _dummyTail != look)
          {
              count++;
              look = look._getNextLink();
          }
          return count;
      }
docs: This is a method used by the unit tests to determine the number of links in the list.
  It's too inefficient for any other purpose.
  
  @return the number of links