Based on patch provided by PR 37017.
Fixes build problem with gtk-2.12.0.
OKed by wiz@.
This release introduces so-called paper mode, a new galculator view intended to
be more intuitive by means of "Do your calculations as you would do them on a
paper". Along with this new GUI feature, various bugs all over the GUI - core
interface have been fixed, with the arithmetic core stable and flawless since a
handful of releases.