An enum for determining where a dropped row goes.
|0||Gtk::TREE_VIEW_DROP_BEFORE||Drop before this row.|
|1||Gtk::TREE_VIEW_DROP_AFTER||Drop after this row.|
|2||Gtk::TREE_VIEW_DROP_INTO_OR_BEFORE||Drop as a child of this row (with fallback to before if into is not possible)|
|3||Gtk::TREE_VIEW_DROP_INTO_OR_AFTER||Drop as a child of this row (with fallback to after if into is not possible)|