I ran into an issue migrating from 9.1 to 9.3 on ubuntu using pg_upgrade
the default ubuntu package, and the one from postgresql.org, both store `postgresql.conf` in etc as
`/etc/postgresql/VERSION/main/postgresql.conf`
however, the pg_upgrade script expects it in the `datadir`.
the simple solution seems to be just symlinking the /etc files into the data dirs.
it took me a while to realize this was the error.
it might make sense to upgrade the docs with a note about what should be in the data dir to enable an upgrade.