Updated stale docstring of setup_joins

        Compute the necessary table joins for the passage through the fields

        given in 'names'. 'opts' is the Options class for the current model

        (which gives the table we are joining to), 'alias' is the alias for the

        table we are joining to. If dupe_multis is True, any many-to-many or

        many-to-one joins will always create a new alias (necessary for

        disjunctive filters). If can_reuse is not None, it's a list of aliases

        that can be reused in these joins (nothing else can be reused in this

        case). Finally, 'negate' is used in the same sense as for add_filter()

        table we are joining to.

        The 'can_reuse' defines the reverse foreign key joins we can reuse. It

        can be either sql.constants.REUSE_ALL in which case all joins are

        reusable or a set of aliases that can be reused. Non-reverse foreign

        keys are always reusable.

        The 'allow_explicit_fk' controls if field.attname is allowed in the

        lookups.

        Finally, 'negate' is used in the same sense as for add_filter()

        -- it indicates an exclude() filter, or something similar. It is only

        passed in here so that it can be passed to a field's extra_filter() for

        customized behavior.