* rsvg-gobject.c: Introduce PRIVATE API to get around bugs 357406 and 362217.
	IMHO, gobject's type registration and quark/error system is fundamentally
	broken with respect to (un)loadable modules such as GTK+ theme engines. This
	is the best I can do for now without breaking librsvg's API. This may cause
	as many headaches as it fixes, though.
	* rsvg-private.h: Declare new _rsvg_register_types() function
	* gtk-engine/svg-main.c: Invoke new type registration function
	* librsvg.def: export this function