introspectable interface doesn't compile

[Rich]

Anyone who #includes core/dbus/interfaces/introspectable.h will get a compile error at the call to invoke_method_synchronously in the method 'introspect()'. The return type of invoke_method_synchronously() does not match the return type of the intropect() call. I believe all that is required is this change:

    std::string introspect()
    {
        return service->root_object()->invoke_method_synchronously<Introspect, std::string>();
    }

to

    std::string introspect()
    {
        return service->root_object()->invoke_method_synchronously<Introspect, std::string>().value();
    }

[Rich (rhvonlehe)]

A test or example that uses this interface would be great. I'm trying to use this interface myself and if successful I might circle back and submit an update to the 'benchmark' example to make it introspectable.