pull request to fix issue #187 columns drag and drop does not work in IE

The fix is to catch 'selectStart' event and call native IE dragDrop() when dragging a column.
https://github.com/Knockout-Contrib/KoGrid/issues/187

The fix was mentioned in here http://stackoverflow.com/questions/5500615/internet-explorer-9-drag-and-drop-dnd

Tested in IE9 and IE10.