title: No gridlines displayed for y3axis in jqPlot
body: <p>Please have a look at this <a href="http://jsfiddle.net/Mumtaz/B8kfS/" rel="nofollow">jsfiddle example</a>.</p>
  
  <pre><code> series: [{
          yaxis: 'yaxis',
          tickOptions: {
              showGridline: true
          }
      }, {
          yaxis: 'y3axis',
          tickOptions: {
              showGridline: true
          }
      }, {
          yaxis: 'yaxis',
          tickOptions: {
              showGridline: true
          }
      }]
  </code></pre>
  
  <p>There are no gridlines against y3axis' ticks.</p>
  
  <p>And also <a href="http://jsfiddle.net/Mumtaz/6vc2u/" rel="nofollow">this example</a>, </p>
  
  <pre><code>series: [{
          yaxis: 'y3axis',           
          tickOptions: {
              showGridline: true
          }
      }, {
          yaxis: 'y3axis',
          tickOptions: {
              showGridline: true
          }
      }, {
          yaxis: 'y3axis',
          tickOptions: {
              showGridline: true
          }
      }]
  </code></pre>
  
  <p>There are no gridlines at all  if all the series are plotted against y3axis. The same is true for y4axis.</p>
  
  <p>Can someone help me with how I can make the gridlines appear for y3axis as well?</p>