gboolean gtk_tree_drag_dest_drag_data_received ( GtkTreeDragDest* drag_dest, GtkTreePath* dest, GtkSelectionData* selection_data )
GtkTreeDragDest to insert a row before the path
deriving the contents of the row from
outside the tree so that inserting before it is impossible,
will be returned. Also,
FALSE may be returned if the new row is
not created for some model-specific reason. Should robustly handle
dest no longer found in the model!