void gtk_tree_selection_set_select_function ( GtkTreeSelection* selection, GtkTreeSelectionFunc func, gpointer data, GDestroyNotify destroy )
Sets the selection function.
If set, this function is called before any node is selected or unselected,
giving some control over which nodes are selected. The select function
TRUE if the state of the node may be toggled, and
if the state of the node should be left unchanged.