title: DBUnit duplicate rows removal
body: <p>Need to know how to remove duplicate rows in dataset .
  I am gathering data from two different databases (all columns are same in both of them) and they have some same rows.</p>
  
  <p>I use <code>QueryDataSet</code> two times. I merge them by using <code>CompositeDataSet</code>.
  Thing I get is list of all rows and some of them are duplicate.</p>
  
  <p>Is there an easy way to delete those duplicates and to order them somehow? 
  Thanks in advance.</p>