add: break;
context: key_release_event (GtkWidget *widget, GdkEventKey *event){    switch (screen.state) {    case NORMAL:	if((event->keyval == GDK_Shift_L) ||	   (event->keyval == GDK_Shift_R)) {	    gdk_window_set_cursor(gtk_widget_get_parent_window(screen.drawing_area),				  GERBV_DEF_CURSOR);	}	break;    case ALT_PRESSED:	if ((event->keyval == GDK_Alt_L) ||	     (event->keyval == GDK_Alt_R)) {	    if ((screen.selected_layer != -1) &&		(screen.selected_layer < MAX_FILES)){		TOGGLE_BUTTON(screen.layer_button[screen.selected_layer]);	    }	    screen.state = NORMAL;	}    default:    }    return TRUE;} /* key_release_event */