* gtk/gtkenums.h: Add GtkArrowPlacement
* gtk/gtkmenu.c (gtk_menu_class_init), (get_arrows_border),
(get_arrows_visible_area), (get_double_arrows),
(get_arrows_sensitive_area): Implement GtkMenu::arrow-placement
to allow scrolling arrows to be placed at the start, end or both
Patch by Tommi Komulainen and myself

svn path=/trunk/; revision=21606