BEAST-GTK: work around GtkSpinButton asserting page-size=0 in adjustments
BEAST-GTK: work around GtkSpinButton asserting page-size=0 in adjustments

swesterfeld/beast,tim-janik/beast,swesterfeld/beast,GNOME/beast,tim-janik/beast,GNOME/beast,tim-janik/beast,GNOME/beast,swesterfeld/beast,swesterfeld/beast,tim-janik/beast,swesterfeld/beast,swesterfeld/beast,GNOME/beast,GNOME/beast,GNOME/beast,tim-janik/beast,GNOME/beast,swesterfeld/beast,tim-janik/beast,tim-janik/beast