pgsql: Add that PL/Java is an implementation of SQL/JRT, and drop claim

Log Message:
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Add that PL/Java is an implementation of SQL/JRT, and drop claim that
PL/pgSQL has much to do with SQL/PSM.

Modified Files:
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pgsql/doc/src/sgml:
features.sgml (r2.28 -> r2.29)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/features.sgml?r1=2.28&r2=2.29)