treeview: Only set focus column in setter function
treeview: Only set focus column in setter function

Single point of entry. It's actually going to become more complicated
with a11y now.

davidgumberg/gtk,Adamovskiy/gtk,Distrotech/gtk2,davidgumberg/gtk,jessevdk/gtk,Adamovskiy/gtk,davidgumberg/gtk,msteinert/gtk,chergert/gtk,msteinert/gtk,davidgumberg/gtk,ahodesuka/gtk,davidgumberg/gtk,davidgumberg/gtk,Sidnioulz/SandboxGtk,ebassi/gtk,jigpu/gtk,ahodesuka/gtk,Sidnioulz/SandboxGtk,chergert/gtk,ebassi/gtk,chergert/gtk,msteinert/gtk,Adamovskiy/gtk,bratsche/gtk-,ebassi/gtk,Sidnioulz/SandboxGtk,Lyude/gtk-,alexlarsson/gtk,jadahl/gtk,ahodesuka/gtk,davidt/gtk,Sidnioulz/SandboxGtk,jigpu/gtk,jessevdk/gtk,chergert/gtk,ahodesuka/gtk,Adamovskiy/gtk,jessevdk/gtk,davidt/gtk,grubersjoe/adwaita,bratsche/gtk-,grubersjoe/adwaita,Adamovskiy/gtk,jadahl/gtk,bratsche/gtk-,jigpu/gtk,jadahl/gtk,Distrotech/gtk2,ahodesuka/gtk,alexlarsson/gtk,ahodesuka/gtk,msteinert/gtk,alexlarsson/gtk,Distrotech/gtk2,Adamovskiy/gtk,Adamovskiy/gtk,ebassi/gtk,jessevdk/gtk,grubersjoe/adwaita,Lyude/gtk-,ahodesuka/gtk,chergert/gtk,jigpu/gtk,grubersjoe/adwaita,jadahl/gtk,davidt/gtk,ebassi/gtk,jessevdk/gtk,Lyude/gtk-,jadahl/gtk,bratsche/gtk-,Distrotech/gtk2,grubersjoe/adwaita,jigpu/gtk,bratsche/gtk-,Adamovskiy/gtk,Sidnioulz/SandboxGtk,bratsche/gtk-,Sidnioulz/SandboxGtk,grubersjoe/adwaita,Lyude/gtk-,Lyude/gtk-,jessevdk/gtk,ebassi/gtk,jadahl/gtk,chergert/gtk,Distrotech/gtk2,Distrotech/gtk2,chergert/gtk,alexlarsson/gtk,grubersjoe/adwaita,grubersjoe/adwaita,Lyude/gtk-,davidgumberg/gtk,jigpu/gtk,jadahl/gtk,davidt/gtk,alexlarsson/gtk,msteinert/gtk,davidgumberg/gtk,Lyude/gtk-,msteinert/gtk,jessevdk/gtk,jadahl/gtk,alexlarsson/gtk,chergert/gtk,ahodesuka/gtk,davidt/gtk,Lyude/gtk-,davidt/gtk,alexlarsson/gtk,jigpu/gtk,jigpu/gtk,alexlarsson/gtk