pgsql: Make PL/Python tests more compatible with Python 3 This changes

Log Message:
-----------
Make PL/Python tests more compatible with Python 3

This changes a bunch of incidentially used constructs in the PL/Python
regression tests to equivalent constructs in cases where Python 3 no longer
supports the old syntax. Support for older Python versions is unchanged.

Modified Files:
--------------
pgsql/src/pl/plpython/expected:
plpython_error.out (r1.7 -> r1.8)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_error.out?r1=1.7&r2=1.8)
plpython_error_2.out (r1.2 -> r1.3)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_error_2.out?r1=1.2&r2=1.3)
plpython_global.out (r1.1 -> r1.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_global.out?r1=1.1&r2=1.2)
plpython_import.out (r1.1 -> r1.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_import.out?r1=1.1&r2=1.2)
plpython_setof.out (r1.2 -> r1.3)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_setof.out?r1=1.2&r2=1.3)
plpython_spi.out (r1.1 -> r1.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_spi.out?r1=1.1&r2=1.2)
plpython_test.out (r1.11 -> r1.12)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_test.out?r1=1.11&r2=1.12)
plpython_trigger.out (r1.2 -> r1.3)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_trigger.out?r1=1.2&r2=1.3)
pgsql/src/pl/plpython/sql:
plpython_error.sql (r1.4 -> r1.5)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_error.sql?r1=1.4&r2=1.5)
plpython_global.sql (r1.1 -> r1.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_global.sql?r1=1.1&r2=1.2)
plpython_import.sql (r1.1 -> r1.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_import.sql?r1=1.1&r2=1.2)
plpython_setof.sql (r1.4 -> r1.5)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_setof.sql?r1=1.4&r2=1.5)
plpython_spi.sql (r1.2 -> r1.3)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_spi.sql?r1=1.2&r2=1.3)
plpython_test.sql (r1.7 -> r1.8)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_test.sql?r1=1.7&r2=1.8)
plpython_trigger.sql (r1.2 -> r1.3)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_trigger.sql?r1=1.2&r2=1.3)