title: Angular UI-grid not sorting by date
body: <p>I am using UI-grid, and I have a bunch of JS date objects like so:</p>
  
  <pre><code>"dob": new Date('1942-11-19')
  </code></pre>
  
  <p>I want to be able to filter the column by date when you click the "sort ascending/descending" buttons. As such, I have set the <code>colDef</code> up like so:</p>
  
  <pre><code>      {
          field: 'dob'
          , displayName: 'D.O.B.'
          , width: '130'
          , editableCellTemplate: '&lt;div&gt;&lt;form name="inputForm"&gt;&lt;input type="INPUT_TYPE" ng-class="\'colt\' + col.uid" ui-grid-editor ng-model="MODEL_COL_FIELD" style="border-bottom-color: #74B3CE; border-bottom-width: 2px;"&gt;&lt;/form&gt;&lt;/div&gt;'
          , headerCellClass: $scope.highlightFilteredHeader
          , cellTemplate: '&lt;div class="ui-grid-cell-contents" &gt;{{grid.getCellValue(row, col)| date:\'MM-dd-yyyy\'}}&lt;/div&gt;'
          , cellFilter: 'date'
          , type: 'date'
        },
  </code></pre>
  
  <p>however, the column simply does not sort correctly. I even tried to set up a function to sort it from an external button like so:</p>
  
  <pre><code>      function mostRecent(){
          console.log('clicked mostRecent');
          $scope.gridApi.grid.sortColumn(
            $scope.gridApi.grid.getColumn('dob'), uiGridConstants.DESC
          );
          $scope.gridApi.grid.notifyDataChange(uiGridConstants.dataChange.ALL); //this line updates the rest of the columns accordingly
        };
  </code></pre>
  
  <p>But it also causes a mish-mush sort that is not correct. Does anyone know what the issue is? I thought it might have to do with my <code>cellTemplate</code>, but after removing the template, there wasn't a difference...</p>