scrolledwindow: Keep scrollbars out of GtkScrollable::get_border
scrolledwindow: Keep scrollbars out of GtkScrollable::get_border

It looks a bit odd that scrollbars stay over treeview headers and
similar, seems nicer to just avoid the border regions.

https://bugzilla.gnome.org/show_bug.cgi?id=751805

alexlarsson/gtk,chergert/gtk,jigpu/gtk,davidgumberg/gtk,alexlarsson/gtk,jigpu/gtk,Adamovskiy/gtk,Adamovskiy/gtk,Adamovskiy/gtk,jadahl/gtk,jigpu/gtk,grubersjoe/adwaita,alexlarsson/gtk,jigpu/gtk,davidgumberg/gtk,jadahl/gtk,grubersjoe/adwaita,chergert/gtk,Adamovskiy/gtk,chergert/gtk,jigpu/gtk,grubersjoe/adwaita,Adamovskiy/gtk,davidgumberg/gtk,chergert/gtk,jadahl/gtk,jadahl/gtk,grubersjoe/adwaita,alexlarsson/gtk,jigpu/gtk,chergert/gtk,jadahl/gtk,grubersjoe/adwaita,Adamovskiy/gtk,grubersjoe/adwaita,davidgumberg/gtk,jadahl/gtk,jadahl/gtk,grubersjoe/adwaita,davidgumberg/gtk,grubersjoe/adwaita,Adamovskiy/gtk,jadahl/gtk,jigpu/gtk,jigpu/gtk,davidgumberg/gtk,alexlarsson/gtk,davidgumberg/gtk,Adamovskiy/gtk,alexlarsson/gtk,chergert/gtk,alexlarsson/gtk,davidgumberg/gtk,chergert/gtk,chergert/gtk,alexlarsson/gtk