pgsql: Minor SGML work: add some more hyperlinks, where appropriate.

Log Message:
-----------
Minor SGML work: add some more hyperlinks, where appropriate.

Modified Files:
--------------
    pgsql/doc/src/sgml/ref:
        commit_prepared.sgml (r1.1 -> r1.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/commit_prepared.sgml.diff?r1=1.1&r2=1.2)
        declare.sgml (r1.36 -> r1.37)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/declare.sgml.diff?r1=1.36&r2=1.37)
        prepare.sgml (r1.18 -> r1.19)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/prepare.sgml.diff?r1=1.18&r2=1.19)
        prepare_transaction.sgml (r1.3 -> r1.4)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/prepare_transaction.sgml.diff?r1=1.3&r2=1.4)
        rollback_prepared.sgml (r1.1 -> r1.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/rollback_prepared.sgml.diff?r1=1.1&r2=1.2)