I was reading through the eel extensions to glib and I noticed these two
functions that seem general and easy enaugh.
Maybe they are worth to be included in glib.
If you are interested I can prepare a patch (with the gtk coding style and
with inline docs)

GList *
g_list_from_g_slist (GSList *slist)
{
	GList *list;
	GSList *node;

	list = NULL;
	for (node = slist; node; node = node->next) {
		list = g_list_prepend (list, node->data);
	}
	return g_list_reverse (list);
}

GSList *
g_slist_from_g_list (GList *list)
{
	GSList *slist;
	GList *node;

	slist = NULL;
	for (node = list; node; node = node->next) {
		slist = g_slist_prepend (slist, node->data);
	}
	return g_slist_reverse (slist);
}