Fix returned rows for grid select() method for grouped data used in grid that is configured with groupable = false.

[Wolfgang]

• in a grid configured to groupable = false
• using a datasource that is grouped will allow selecting a grouping row, it does not show in the ui, but the select() method will return the grouping row. 

demo: 
http://dojo.telerik.com/aDevo

[Nikolay Rusev]

Hello Wolfgang,

Indeed change should not be triggered for grouping rows and select method should return them as well. 

This issue is caused due to performance optimization of the selectors that are being passed to Selectable widget. The code relies on `groupable` option of the Grid to detect whether to build more complex selector.

Thank you for bringing our attention to this issue. We will investigate further how to address this. 

Regards,
Nikolay Rusev
Telerik