It seems to me that this code in pg_upgrade/check.c has been useless
since at least version 9.1:
/* Is it 9.0 but without tablespace directories? */
if (GET_MAJOR_VERSION(new_cluster.major_version) == 900 &&
new_cluster.controldata.cat_ver < TABLE_SPACE_SUBDIRS_CAT_VER)
pg_fatal("This utility can only upgrade to PostgreSQL version
9.0 after 2010-01-11\n"
"because of backend API changes made during
development.\n");
--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services