title: dataTables (jquery) search by two columns
body: <p>I want to search table by only two columns. E.g. Initial search searches in all columns, I just want to search by two columns.
  When I use following code: </p>
  
  <pre><code>dataTable.columns([1,7])
      .search("some string")
      .draw(); 
  </code></pre>
  
  <p>the search text must be present in both columns to be displayed. I want to display it even if it exists in one of the columns. Can anyone help?</p>
  
  <p>Thanks</p>