pgsql: Update 8.1 and 8.0 plpython to work with Python 2.5.

Log Message:
-----------
Update 8.1 and 8.0 plpython to work with Python 2.5. This backports several
fixes made during the 8.2 development cycle, but not backported at the time
for lack of confidence in the new coding.

I didn't touch 7.4 because it has more problems than this: the configure
probe for Python fails.

Tags:
----
REL8_0_STABLE

Modified Files:
--------------
pgsql/src/pl/plpython:
plpython.c (r1.58.4.7 -> r1.58.4.8)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/plpython.c?r1=1.58.4.7&r2=1.58.4.8)
plpython_function.sql (r1.6.8.1 -> r1.6.8.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/plpython_function.sql?r1=1.6.8.1&r2=1.6.8.2)