pgsql: Update 9.0 release notes so streaming replication and hot standby

Log Message:
-----------
Update 9.0 release notes so streaming replication and hot standby is not
assumed to require continuous archiving.

Per report from Fujii Masao

Modified Files:
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pgsql/doc/src/sgml:
release-9.0.sgml (r2.37 -> r2.38)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/release-9.0.sgml?r1=2.37&r2=2.38)