Enable locale-aware index on the artist list

Ported code of PR#1229 from GitHub. This almost works, except for one blocker: the artist list should be sorted lexicographically in the form (index_of(artist_name), artist_name) using locale.strcoll. I attempted to hack SelectionList.__sort_items, but it never worked.

    # One of my attempts...
    def __sort_items(self, model, itera, iterb, data):
        """
            Sort model
        """
        if not self.__updating:
            return False

        a_index = model.get_value(itera, 0)
        b_index = model.get_value(iterb, 0)

        # Static vs static
        if a_index < 0 and b_index < 0:
            return a_index < b_index
        # Static entries always on top
        elif b_index < 0:
            return True
        # Static entries always on top
        if a_index < 0:
            return False
        # String comparaison for non static
        else:
            if self.__is_artists:
                a = Lp().artists.get_sortname(a_index)
                b = Lp().artists.get_sortname(b_index)
            else:
                a = model.get_value(itera, 1)
                b = model.get_value(iterb, 1)
            ia = index_of(a).upper()
            ib = index_of(b).upper()
            if strcoll(ia, ib) < 0: return -1
            elif strcoll(ia, ib) == 0: return strcoll(a, b)
            else: return 1

Can you give me some hints on how to solve this problem? Thanks.