fixes #786 Shift + row select highlights outside text (ie)

`ms-user-select: none;` will block selection from starting on the element.
It will not block an existing selection from entering the element. [reference](http://ie.microsoft.com/TestDrive/HTML5/msUserSelect/Default.html)

When using the shift modifier IE will select everything from the top of
the document, or last clicked location, up until the shift-clicked
location. Since the selection starts outside of the element marked with
ms-user-select: none; all of the text is selected.

Added a check for `msUserSelect`, and fallback to other methods to stop
selection.

fixes: https://github.com/SitePen/dgrid/issues/786