title: Highchart datetime x-axis : display end of month date instead of first day of month
body: <p>In my chart, I try to display end of month performances over one year (at 31 Jan, 29 Fev, ..., 31 Dec). X-axis is defined as follow:</p>
  
  <pre><code>xAxis: {
      type: 'datetime',
          dateTimeLabelFormats: {
              month: '%b %Y'
          }
      }
  }
  </code></pre>
  
  <p>The issue is that the scale automatically adjust to the appropriate unit (Months) and display the first day of the Month. As a result, my first element (at 31 Jan) is displayed above "Feb 2012" (same issue for other elements).
  I was wondering if I could rather display the end of month day on my x-axis. Any idea?</p>
  
  <p>Thanks,</p>
  
  <p><a href="http://jsfiddle.net/j8Bec/" rel="nofollow">Example</a></p>