Per SQL:202x draft, in the CYCLE clause of a recursive query, the
cycle mark values can be of type boolean and can be omitted, in which
case they default to TRUE and FALSE.
Reviewed-by: Vik Fearing <vik@postgresfriends.org>
Discussion: https://www.postgresql.org/message-id/flat/db80ceee-6f97-9b4a-8ee8-3ba0c58e5be2@2ndquadrant.com