Convert the rest of the error and warning dialogs to Gtk::MessageDialog since it...
drwxr-xr-x - ETL
drwxr-xr-x - autobuild
drwxr-xr-x - gtkmm-osx
drwxr-xr-x - synfig-core
drwxr-xr-x - synfig-osx
drwxr-xr-x - synfig-studio