title: Format jqPlot pointLabels to currency
body: <p>I am trying to get the commas in my values.</p>
  
  <p>so far I can get the $, but nothing else:</p>
  
  <pre><code>                seriesDefaults: {
                      renderer: $.jqplot.BarRenderer,
                      pointLabels: { show: true, formatString: '$%s' },
                  },
  </code></pre>
  
  <p>Is there a way to get a pointLabel to look like <strong>$45,666,444</strong> ?</p>