Removed use of SortedDict for query.alias_refcount

    def __init__(self, model, where=WhereNode):

        self.model = model

        self.alias_refcount = SortedDict()

        self.alias_refcount = {}

        # alias_map is the most important data structure regarding joins.

        # It's used for recording which joins exist in the query and what

        # type they are. The key is the alias of the joined table (possibly

        count. Note that after execution, the reference counts are zeroed, so

        tables added in compiler will not be seen by this method.

        """

        return len([1 for count in six.itervalues(self.alias_refcount) if count])

        return len([1 for count in self.alias_refcount.values() if count])

    def join(self, connection, always_create=False, exclusions=(),

            promote=False, outer_if_first=False, nullable=False, reuse=None):

        # comparison to NULL (e.g. in

        # Tag.objects.exclude(parent__parent__name='t1'), a tag with no parent

        # would otherwise be overlooked).

        active_positions = [pos for (pos, count) in

                enumerate(six.itervalues(query.alias_refcount)) if count]

        if active_positions[-1] > 1:

        active_positions = len([count for count

                                in query.alias_refcount.items() if count])

        if active_positions > 1:

            self.add_filter(('%s__isnull' % prefix, False), negate=True,

                    trim=True, can_reuse=can_reuse)