title: Display empty string in xaxis with jqplot
body: <p>I using jqplot for my line chart, I have 2 field in data [date, int],my json data here: </p>
  
  <pre><code>[{"12/15/2013": "10"},{"12/16/2013": "0"}, {"12/22/2013": "10"},{"12/29/2013": "0"},{"12/30/2013": "10"}] 
  </code></pre>
  
  <ul>
  <li>In this data, days 15, 22, 29 in Dec is sunday, i want display in xaxis label. </li>
  <li>with days 16, 30 in Dec, i dont want display in xaxis, but in yaxis should be display point label. </li>
  </ul>
  
  <p>My problem i cant find how to do that, anyone can suggest me anyway.
  Thank</p>