path from selection data of target type gtk_tree_model_row
Normally called from a drag_data_received handler. This function can only be used if
selection_data originates from the same
process that’s calling this function, because a pointer to the tree model is being passed around. If you aren’t in the same process, then
you'll get memory corruption. In the TreeDragDest drag_data_received handler,
you can assume that selection data of type gtk_tree_model_row is in from the current process. The returned
path must be freed with free.