Change the special code for handling GObject and GInitiallyUnowned
so that it exposes GParamSpec as a class, and it allows GVariant to
have a GType without using the deprecate g_variant_get_gtype.
It is a sort of ABI break, in that new typelibs won't work with
previous versions of libgirepository.
https://bugzilla.gnome.org/show_bug.cgi?id=646635