gtk2: (maybe) fix wrong property value on ppc64 and s390x
gtk2: (maybe) fix wrong property value on ppc64 and s390x

GitHub: fixes #256

Reported by mtasaka. Thanks!!!

kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2