code: byte[] getFirstKey(TableKelp table)
    {
      int keyOffset = table.getKeyOffset();
      int keyLength = table.getKeyLength();
      
      int offset = _rowHead + keyOffset;
      
      byte []key = new byte[keyLength];
      byte []buffer = getBuffer();
      
      System.arraycopy(buffer, offset, key, 0, keyLength);
      
      return key;
    }
docs: Returns the first key in the block.
  
  XXX: ??? since the keys are unsorted, why is this valuable