title: Highstock tickPixelInterval is not working
body: <p>I have an issue with tickPixelInterval of highstock.
      When we click on the Zoom buttons, accordingly the data should be shown.
      If we click on Day(1d) button, it should exactly show the one day data and date format on x-Axis should start with 00:00 and end date with 23:59, the time interval must be one hour.
  If we click on the 1M,3M,6M buttons, it should display the data accordingly, and the date format/Interval on X-Axis  interval must be one day.
  Is it Possible with Highstock? Here in <a href="http://jsfiddle.net/fe83S/1/" rel="nofollow">JSFiddle</a>
      How can we increase length of the x-axis?</p>
  
  <pre><code>    $(function() {
      $.getJSON('http://www.highcharts.com/samples/data/jsonp.php?filename=aapl-c.json&amp;callback=?', function(data) {
  
          // Create the chart
          $('#container').highcharts('StockChart', {
  
  
              rangeSelector : {
  
              inputEnabled: $('#container').width() &gt; 280,
              buttons: [{
                  type: 'day',
                  count: 5,
                  text: '1d'
              }, {
                  type: 'month',
                  count: 1,
                  text: '1m'
              }, 
              {
                  type: 'month',
                  count: 3,
                  text: '3m'
              },
              {
                  type: 'month',
                  count: 6,
                  text: '6m'
              }, {
                  type: 'year',
                  count: 1,
                  text: '1y'
              }, {
                  type: 'all',
                  text: 'All'
              }],
              selected: 0//default show the last 5day's graph
  
              },
  
              title : {
                  text : 'AAPL Stock Price'
              },
              xAxis: {
           type: 'datetime',
           ordinal: false,
           tickInterval: 24*60 * 60 * 1000,//For One Day
           minTickInterval: 60 * 60 * 1000,//For One Hour
           tickPixelInterval: 300,
           startOnTick:true,
  
      },
                scrollbar: {
              //height: 10,
              enable: true
          },
              series : [{
                  name : 'AAPL Stock Price',
                  data : data,
                  marker : {
                      enabled : true,
                      radius : 3
                  },
                  shadow : true,
                  tooltip : {
                      valueDecimals : 2
                  },
                 pointInterval: 24*60*60*1000 
              }]
          });
      });
  });
  </code></pre>