Request to support new roles when validating route relations.

[pelderson@…]

Five new roles have been approved for route relations. See ​https://wiki.openstreetmap.org/wiki/Proposed_features/Recreational_route_relation_roles

The roles are: alternative, approach, excursion, connection, main.
No role is the same as main for data users, but the explicit value main is now an approved value.

Validation currently warns about roles other than forward, backward, and guidepost for members of route relations.

We would appreciate if the new role values could become accepted by the standard validation rules.