pgsql: Restrict pg_relation_size to relation owner, pg_database_size to

Log Message:
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Restrict pg_relation_size to relation owner, pg_database_size to DB owner,
and pg_tablespace_size to superusers.  Perhaps we could weaken the first
case to just require SELECT privilege, but that doesn't work for the
other cases, so use ownership as the common concept.

Modified Files:
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    pgsql/src/backend/utils/adt:
        dbsize.c (r1.12 -> r1.13)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/dbsize.c?r1=1.12&r2=1.13)