pgsql: Add mention that pg_ctl will return an accurate exit code when

Log Message:
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Add mention that pg_ctl will return an accurate exit code when waiting
for startup or shutdown. We have always done this but it wasn't documented.

Modified Files:
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pgsql/doc/src/sgml/ref:
pg_ctl-ref.sgml (r1.29 -> r1.30)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/pg_ctl-ref.sgml.diff?r1=1.29&r2=1.30)