pgsql: doc: mention datadir locations are actually config locations

doc: mention datadir locations are actually config locations

Technically, pg_upgrade's --old-datadir and --new-datadir are
configuration directories, not necessarily data directories. This is
reflected in the 'postgres' manual page, so do the same for pg_upgrade.

Reported-by: Yves Goergen

Bug: 14898

Discussion: /messages/by-id/20171110220912.31513.13322@wrigleys.postgresql.org

Backpatch-through: 10

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e5dede90971d2ddbb7bca72ffc329c043bf717db

Modified Files
--------------
doc/src/sgml/ref/pgupgrade.sgml | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)