Clarify pg_rewind connection requirements.
Clarify pg_rewind connection requirements.

Per http://www.postgresql.org/message-id/flat/564C4CE6.9000509@postgrespro.ru
Pavel Luzanov <p.luzanov@postgrespro.ru>

zeroae/postgres-xl,zeroae/postgres-xl,zeroae/postgres-xl,zeroae/postgres-xl,zeroae/postgres-xl