title: Why is ng-grid not sorting by both columns?
body: <p>I have 2 grids showing the same data with 2 different sorts:</p>
  
  <pre><code>$scope.aGridOptions = {
    data: 'aData',
    columnDefs: [
      { displayName: 'Column 1', field: 'col1',}, 
      { displayName: 'Column2',  field: 'col2',}],
    sortInfo: {
      fields: ['col1'], directions: ['asc']
    },
  };
  $scope.bGridOptions = {
    data: 'aData',
    columnDefs: [
      { displayName: 'Column 1', field: 'col1',}, 
      { displayName: 'Column2',  field: 'col2',}],
    sortInfo: {
      fields: ['col1', 'col2'],
      directions: ['asc', 'asc']
    },
  };
  </code></pre>
  
  <p>As the plunker shows, both sort the same way, only by column 1.  Not only that, but ng-grid 2.0.7, trashes by sortInfo object on <code>bGridOptions</code> to shorten the sort to only one column.</p>
  
  <p><a href="http://plnkr.co/edit/riDzDcS3YSJrQrULwL2j?p=preview" rel="nofollow">http://plnkr.co/edit/riDzDcS3YSJrQrULwL2j?p=preview</a></p>
  
  <p>I can't seem to find where it is destroying my sort options.  How do I get it to sort by 2 columns and not have it trash my sortInfo?</p>