Remove double call to Object::as.
Remove double call to Object::as.

	Improves global urbiscript performances by ~1-2%.

	* include/urbi/object/cxx-object.hxx: is_a and as are the same
	thing.

aldebaran/urbi,urbiforge/urbi,urbiforge/urbi,aldebaran/urbi,urbiforge/urbi,urbiforge/urbi,urbiforge/urbi,urbiforge/urbi,aldebaran/urbi,urbiforge/urbi,urbiforge/urbi,aldebaran/urbi,aldebaran/urbi,aldebaran/urbi,aldebaran/urbi,urbiforge/urbi,aldebaran/urbi