pgsql: Use generic attribute management in PL/Python Switch the

Log Message:
-----------
Use generic attribute management in PL/Python

Switch the implementation of the plan and result types to generic attribute
management, as described at <http://docs.python.org/extending/newtypes.html>.
This modernizes and simplifies the code a bit and prepares for Python 3.1,
where the old way doesn't work anymore.

Modified Files:
--------------
    pgsql/src/pl/plpython:
        plpython.c (r1.125 -> r1.126)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/plpython.c?r1=1.125&r2=1.126)
    pgsql/src/pl/plpython/expected:
        plpython_spi.out (r1.2 -> r1.3)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_spi.out?r1=1.2&r2=1.3)
    pgsql/src/pl/plpython/sql:
        plpython_spi.sql (r1.3 -> r1.4)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_spi.sql?r1=1.3&r2=1.4)