pgsql: Augment test coverage in PL/Python, especially for error

Log Message:
-----------
Augment test coverage in PL/Python, especially for error conditions.

Modified Files:
--------------
pgsql/src/pl/plpython:
plpython.c (r1.123 -> r1.124)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/plpython.c?r1=1.123&r2=1.124)
pgsql/src/pl/plpython/expected:
plpython_params.out (r1.1 -> r1.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_params.out?r1=1.1&r2=1.2)
plpython_record.out (r1.1 -> r1.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_record.out?r1=1.1&r2=1.2)
plpython_schema.out (r1.4 -> r1.5)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_schema.out?r1=1.4&r2=1.5)
plpython_setof.out (r1.1 -> r1.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_setof.out?r1=1.1&r2=1.2)
plpython_test.out (r1.10 -> r1.11)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_test.out?r1=1.10&r2=1.11)
plpython_trigger.out (r1.1 -> r1.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_trigger.out?r1=1.1&r2=1.2)
pgsql/src/pl/plpython/sql:
plpython_params.sql (r1.1 -> r1.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_params.sql?r1=1.1&r2=1.2)
plpython_record.sql (r1.1 -> r1.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_record.sql?r1=1.1&r2=1.2)
plpython_schema.sql (r1.4 -> r1.5)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_schema.sql?r1=1.4&r2=1.5)
plpython_setof.sql (r1.3 -> r1.4)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_setof.sql?r1=1.3&r2=1.4)
plpython_spi.sql (r1.1 -> r1.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_spi.sql?r1=1.1&r2=1.2)
plpython_test.sql (r1.6 -> r1.7)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_test.sql?r1=1.6&r2=1.7)
plpython_trigger.sql (r1.1 -> r1.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_trigger.sql?r1=1.1&r2=1.2)