gtk/print.go
func (ps *PrintSettings) SetDuplex(duplex PrintDuplex) {
	C.gtk_print_settings_set_duplex(ps.native(), C.GtkPrintDuplex(duplex))
}
func (ps *PrintSettings) SetDuplex(duplex PrintDuplex) {
	C.gtk_print_settings_set_duplex(ps.native(), C.GtkPrintDuplex(duplex))
}
// SetDuplex() is a wrapper around gtk_print_settings_set_duplex().