Add macros for registering value transformations
@ebassi
Submitted by Emmanuele Bassi Link to original bug (#632448)
Description
Clutter has various boxed types which register GValue transformation functions; in order to switch to G_DEFINE_BOXED_TYPE_WITH_CODE() we had to add a couple of new macros for that. It would be good to have them in upstream GObject, since they use the GType variable name defined by the other G_DEFINE_* macros.