I think a little initcode option would be good on functions, to allow
a bit of code to be inserted at the start.

        * build-guile-gtk-1.2 (emit-funcs): Add "initcode" option to insert
        code at the start of a function.

For instance,

	(define-func gdk_pixbuf_render_threshold_alpha
	  none
	  ((GdkPixbuf pixbuf)
	   (GdkWindow bitmap)
	   (int src_x)
	   (int src_y)
	   (int dest_x)
	   (int dest_y)
	   (int width)
	   (int height)
	   (int alpha_threshold))
	  (initcode "gdk_rgb_init()"))

And similarly for the main gdkrgb functions.