pgsql: Clarify object ownership language to prevent confusion with

Log Message:
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Clarify object ownership language to prevent confusion with database
ownership.

Modified Files:
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pgsql/doc/src/sgml:
user-manag.sgml (r1.27 -> r1.28)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/user-manag.sgml.diff?r1=1.27&r2=1.28)