Revert "PL/Python: Remove workaround for returning booleans in Python <2.3"
Revert "PL/Python: Remove workaround for returning booleans in Python <2.3"

This reverts commit be0dfbad3671ed2503a2a661e70b48c5b364e069.

The previous information that Py_RETURN_TRUE and Py_RETURN_FALSE are
supported in Python 2.3 is wrong.  They require Python 2.4.  Update the
comment about that.

Postgres-XL/Postgres-XL,adam8157/gpdb,ovr/postgres-xl,jmcatamney/gpdb,lisakowen/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,lisakowen/gpdb,greenplum-db/gpdb,adam8157/gpdb,greenplum-db/gpdb,50wu/gpdb,adam8157/gpdb,pavanvd/postgres-xl,ovr/postgres-xl,yazun/postgres-xl,pavanvd/postgres-xl,ashwinstar/gpdb,xinzweb/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,zeroae/postgres-xl,oberstet/postgres-xl,ashwinstar/gpdb,ashwinstar/gpdb,xinzweb/gpdb,xinzweb/gpdb,techdragon/Postgres-XL,greenplum-db/gpdb,greenplum-db/gpdb,adam8157/gpdb,ashwinstar/gpdb,lisakowen/gpdb,ashwinstar/gpdb,xinzweb/gpdb,lisakowen/gpdb,techdragon/Postgres-XL,50wu/gpdb,oberstet/postgres-xl,oberstet/postgres-xl,50wu/gpdb,jmcatamney/gpdb,oberstet/postgres-xl,50wu/gpdb,xinzweb/gpdb,jmcatamney/gpdb,ovr/postgres-xl,techdragon/Postgres-XL,Postgres-XL/Postgres-XL,Postgres-XL/Postgres-XL,lisakowen/gpdb,oberstet/postgres-xl,zeroae/postgres-xl,50wu/gpdb,yazun/postgres-xl,ovr/postgres-xl,jmcatamney/gpdb,adam8157/gpdb,xinzweb/gpdb,yazun/postgres-xl,50wu/gpdb,xinzweb/gpdb,Postgres-XL/Postgres-XL,adam8157/gpdb,adam8157/gpdb,techdragon/Postgres-XL,zeroae/postgres-xl,ovr/postgres-xl,yazun/postgres-xl,Postgres-XL/Postgres-XL,ashwinstar/gpdb,yazun/postgres-xl,adam8157/gpdb,xinzweb/gpdb,pavanvd/postgres-xl,techdragon/Postgres-XL,pavanvd/postgres-xl,50wu/gpdb,lisakowen/gpdb,50wu/gpdb,lisakowen/gpdb,lisakowen/gpdb,greenplum-db/gpdb,pavanvd/postgres-xl,ashwinstar/gpdb,ashwinstar/gpdb,zeroae/postgres-xl,zeroae/postgres-xl,greenplum-db/gpdb,greenplum-db/gpdb