EZ_SetDragIcon sets up a drag icon for the current DnD
operation. It is meant to be used by the initialization procedure
of the drag source. The DnD system resets drag icon to NULL when
the current DnD transaction finishes. There are two possible display
styles for the drag icon, repsented by 0 and 1. When set to 1, the
drag icon will be displayed using the XOR logical function.
EZ_SetDragIcon sets the current drag cursor. Drag cursor
takes procedence over drag icon.