* gtk/gtkwidget.c (gtk_widget_class_init): added ::scroll-arrow-hlength and ::scroll-arrow-vlength style properties. fixed upper limit for ::separator-width and ::separator-height to be MAXINT.
* gtk/gtknotebook.c: use GtkWidget::scroll-arrow-vlength and GtkWidget::scroll-arrow-hlength to determine scroll arrow sizes. added GtkNotebook::arrow-spacing style property to configure the spacing between scroll arrows.