Fixed an issue where the selected class is not applied to new visible columns

Reproducing the issue by using ["Checkbox row select column" example](http://mleibman.github.io/SlickGrid/examples/example-checkbox-row-select.html):

1. Right click header row and unselect **A** column.
2. Select **Row 0** by clicking the checkbox before text "Row 0".
3. Right click header row and select **A** column.

The cell with text "Row 0" is not highlighted.  (See the following snapshot)

![image 1](https://cloud.githubusercontent.com/assets/4248581/4907030/dd33a2e0-645d-11e4-9fdc-46207d20b8fc.jpg)

Similar issue was reported here:
" #892 After `setColumns` selected class is not applied to new columns"