pgsql: Add some basic regression tests for refcursors in PL/PgSQL.

Log Message:
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Add some basic regression tests for refcursors in PL/PgSQL.

Modified Files:
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pgsql/src/test/regress/expected:
plpgsql.out (r1.24 -> r1.25)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/plpgsql.out.diff?r1=1.24&r2=1.25)
pgsql/src/test/regress/sql:
plpgsql.sql (r1.19 -> r1.20)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/plpgsql.sql.diff?r1=1.19&r2=1.20)