pgsql: Back-patch some plpython patches previously made only in HEAD:

Log Message:
-----------
Back-patch some plpython patches previously made only in HEAD: changes of
3-Apr and 4-Apr to declare interface functions properly and eliminate casts,
thereby fixing potential problems on 64-bit machines; and changes of 13-Jul
to volatile-qualify some variables to suppress compiler warnings.
Per discussion, we're only worrying about Python 2.5 in PG 8.2 and up,
so no need to patch further back.

Tags:
----
REL8_2_STABLE

Modified Files:
--------------
    pgsql/src/pl/plpython:
        plpython.c (r1.90.2.1 -> r1.90.2.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/plpython.c?r1=1.90.2.1&r2=1.90.2.2)