librsvg: update to newer API

Certain calls to functions such as rsvg_handle_get_dimensions() and
rsvg_handle_render_cairo() have been deprecated since version 2.52, yet
we've not bothered to keep up to date with the changes to the API.

Change this, but keep backwards compatibility for older librsvg
installations.

Fixes #974

libs/PictureImageLoader.c

@@ -284,7 +284,23 @@ Bool PImageLoadSvg(FIMAGE_CMD_ARGS)
 	free(allocated_path);
 
 	/* Keep the original aspect ratio when either w or h is 0 */
+#if LIBRSVG_CHECK_VERSION(2,52,0)
+	double		ddw, ddh;
+	RsvgLength	out_w, out_h;
+
+	rsvg_handle_get_intrinsic_size_in_pixels(rsvg, &ddw, &ddh);
+	dim.width = ddw;
+	dim.height = ddh;
+
+	rsvg_handle_get_intrinsic_dimensions(rsvg, NULL, &out_w, NULL, &out_h,
+		NULL, NULL);
+
+	dim.em = out_w.length;
+	dim.ex = out_h.length;
+
+#else
         Frsvg_handle_get_dimensions(rsvg, &dim);
+#endif
 	if (!w && !h)
 	{
 		w = dim.width;
@@ -357,7 +373,19 @@ Bool PImageLoadSvg(FIMAGE_CMD_ARGS)
 	Fcairo_translate(cr, -.5, -.5);
 	Fcairo_scale(cr, 1 / dim.em, 1 / dim.ex);
 
+#if LIBRSVG_CHECK_VERSION(2,52,0)
+	GError *err = NULL;
+	RsvgRectangle vp;
+
+	vp.x = 0;
+	vp.y = 0;
+	vp.width = dim.width;
+	vp.height = dim.height;
+
+	rsvg_handle_render_document(rsvg, cr, &vp, &err);
+#else
 	Frsvg_handle_render_cairo(rsvg, cr);
+#endif
 	Fg_object_unref(FG_OBJECT(rsvg));
 	Fcairo_destroy(cr);