printing: Show "Replace" button when printing to existing file
printing: Show "Replace" button when printing to existing file

Use gtk_dialog_add_button() which adds the button to
the message dialog correctly and uses gtk_widget_show() on it.

jadahl/gtk,Sidnioulz/SandboxGtk,jadahl/gtk,jessevdk/gtk,Sidnioulz/SandboxGtk,ahodesuka/gtk,ahodesuka/gtk,davidgumberg/gtk,jadahl/gtk,Adamovskiy/gtk,Adamovskiy/gtk,jadahl/gtk,davidgumberg/gtk,chergert/gtk,chergert/gtk,chergert/gtk,ahodesuka/gtk,davidgumberg/gtk,ahodesuka/gtk,Sidnioulz/SandboxGtk,chergert/gtk,Adamovskiy/gtk,Adamovskiy/gtk,msteinert/gtk,grubersjoe/adwaita,Lyude/gtk-,grubersjoe/adwaita,Adamovskiy/gtk,Lyude/gtk-,Lyude/gtk-,alexlarsson/gtk,grubersjoe/adwaita,msteinert/gtk,alexlarsson/gtk,alexlarsson/gtk,alexlarsson/gtk,jigpu/gtk,chergert/gtk,msteinert/gtk,davidgumberg/gtk,Lyude/gtk-,jessevdk/gtk,Lyude/gtk-,davidgumberg/gtk,msteinert/gtk,jessevdk/gtk,jigpu/gtk,Sidnioulz/SandboxGtk,chergert/gtk,davidgumberg/gtk,alexlarsson/gtk,ahodesuka/gtk,davidgumberg/gtk,Sidnioulz/SandboxGtk,msteinert/gtk,jessevdk/gtk,jadahl/gtk,msteinert/gtk,grubersjoe/adwaita,jigpu/gtk,grubersjoe/adwaita,grubersjoe/adwaita,jigpu/gtk,Lyude/gtk-,Lyude/gtk-,jigpu/gtk,jadahl/gtk,chergert/gtk,davidgumberg/gtk,jessevdk/gtk,jadahl/gtk,alexlarsson/gtk,alexlarsson/gtk,grubersjoe/adwaita,jessevdk/gtk,Lyude/gtk-,jadahl/gtk,jessevdk/gtk,Adamovskiy/gtk,alexlarsson/gtk,Adamovskiy/gtk,ahodesuka/gtk,jigpu/gtk,Adamovskiy/gtk,chergert/gtk,Sidnioulz/SandboxGtk,jigpu/gtk,ahodesuka/gtk,jigpu/gtk,grubersjoe/adwaita,ahodesuka/gtk