Solving issue 794 (yet again :)) : RT themes don't work well in Ubuntu 11.04

Thanks goes to GreatBull who found the solution.
This patch also force the icons to be displayed in the buttons for the Linux system (already worked fine on Windows)

rtgui/main.cc

@@ -124,6 +124,16 @@ int main(int argc, char **argv)
    }
    Gtk::Main m(&argc, &argv);
 
+#ifndef _WIN32
+   // For an unknown reason, gtkmm 2.22 don't know the gtk-button-images property, while it exists in the documentation...
+   // Anyway, the problem was Linux only
+   static Glib::RefPtr<Gtk::Settings> settings = Gtk::Settings::get_default();
+   if (settings)
+      settings->property_gtk_button_images().set_value(true);
+   else
+      printf("Error: no default settings to update!\n");
+#endif
+
    RTWindow *rtWindow = new class RTWindow();
    gdk_threads_enter ();
    m.run(*rtWindow);