createClass API in gupnp-av

[Jens Georg <mail jensge org>]

Hi,

apparently upnp:createClass@includeDerived is mandatory. The current
code doesn't include it at all.

While the adding case is easy to fix API-friendly by add_create_class
setting default value for it and add add_create_class_full which allows
to specify the desired value. That would already satisfy our current
needs with Rygel.

The get_create_classes case is a bit more difficult. Add another
function that returns a List of { string, bool } ?

We don't use that function in Rygel and I don't really know if anyone
else does.

Regards,
	Jens