columnview: Make sure focus can move into cells

The cells themselves should never be focusable though.

gtk/gtkcolumnviewcell.c

@@ -143,7 +143,7 @@ gtk_column_view_cell_init (GtkColumnViewCell *self)
 {
   GtkWidget *widget = GTK_WIDGET (self);
 
-  gtk_widget_set_can_focus (widget, FALSE);
+  gtk_widget_set_focusable (widget, FALSE);
   /* FIXME: Figure out if settting the manager class to INVALID should work */
   gtk_widget_set_layout_manager (widget, NULL);
   widget->priv->resize_func = gtk_column_view_cell_resize_func;