As discussed on IRC, we often get questions about failures that occur because people forget to call the library's init() function so the Glib::wrap system doesn't work.  It was suggested that we change the warning message that is printed to the console to make this more explicit.  My stab at a possible wording:
    g_warning("Failed to wrap object of type '%s' (Hint: this error is commonly caused by failing to call a library init() function)", typename);

I plan to commit this unless there are any better suggestions.