Log Message:
Update psycopg to 1.1.21. Allow building with Python 2.4.

>From NEWS:
psycopg news for 1.1.20
-----------------------

* Fixed problem with wrongly applied infinity patch in 1.1.20.

* Fixed build problem in win32 when using Makefile.msvc.

psycopg news for 1.1.20
-----------------------

* Fixed the date/time/timestamp formatting problem introduced by 1.1.19.

* Fixed build problem in win32 when using Makefile.msvc.

psycopg news for 1.1.19
-----------------------

* Now ZPsycopgDA does not loose the connection and raise an error is
  PostgreSQL is restarted but tries to rconnect and execute the issue
  query again (patch from Jonathan Stoneman.)

* Fixed precision and scale in cursor.description for numeric types.

* The XXXFromMx() functions don't truncate fractional seconds anymore (but
  note that mx.DateTime uses floating point seconds so rounding errors may
  creep in anyway.)

* Fixed two segfaults: when multithreading; patch from James Henstridge and
  when calling dictfetchone() without results.

psycopg news for 1.1.18
-----------------------

* Fixed mktime() overflow in ZPsycopgDA.

psycopg news for 1.1.17
-----------------------

* ZPsycopgDA can now return unicode strings on request.

* Fixed problem with timestamps in ZPsycopgDA.

psycopg news for 1.1.16
-----------------------

* fixed .rowcount problem introduced in 1.1.15.

* fixed a problem with %% not being transformed into % when calling
  .execute() with a zero-length tuple or dict.

* now using COPY FROM/COPY TO in .execute() raise an exception instead
  of segfaulting.

* faster Date and DateTime type casting.

* small and trivial optimizations and fixes.

psycopg news for 1.1.15
-----------------------

* Interval typecasting eventually-eventually works the Right Way (TM).

* Fixed two bad memory leaks in QuotedString and Binary objects.

* Reverted change on rowcount attribute, now it is always set to the real
  number of affected columns.
psycopg news for 1.1.14
-----------------------

* Interval typecasting eventually works the Right Way (TM).

* ZPsycopgDA now support unicode strings and different backend encodings.

* ZPsycopgDA accept query data as an extra parameter to execute() (but
  still no way to give it extra data from inside a ZSQL Method.)

* Better DBAPI-2.0 compliance (rowcount attribute and argument passing.)

* Now builds on Fedora Core 2 (but remember that the real psycopg
  aficionado runs on Debian ;-P )

* COPY FROM raise an exception and return usefull information on error.