UnboundColumns
------------------------------------------------------------------------
Additional support for unbound columns.

Instead of using OwnerDraw code to add content to unbound columns, you
can take advantage of the GetUnboundValue and SetUnboundValue events.

The sample binds the grid to a regular DataTable, then adds an
unbound column. The GetUnboundValue and SetUnboundValue events are used
to store and retrieve the unbound values associated with each data row.