Really make britney2 work with python 2.5

PyDict_Next()'s ppos argument should be a Py_ssize_t, not an int.  With
this change, britney2 no longer believes that all packages are
uninstallable.

britney.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python2.4
+#!/usr/bin/python2.5
 # -*- coding: utf-8 -*-
 
 # Copyright (C) 2001-2008 Anthony Towns <ajt@debian.org>

lib/britney-py.c

@@ -1,6 +1,4 @@
-// XXX Please notify DSA once britney2 moves to Python2.5, so that
-// they can uninstall python2.4-dev from ftp-master.
-#include <python2.4/Python.h>
+#include <python2.5/Python.h>
 
 #include "dpkg.h"
 
@@ -945,7 +943,7 @@ static PyObject *apt_versioncmp(PyObject *self, PyObject *args) {
  ******************************************************/
 
 static PyObject *build_system(PyObject *self, PyObject *args) {
-    int pos = 0;
+    Py_ssize_t pos = 0;
     char *arch;
 	PyObject *pkgs, *key, *value, *pyString;