Remove support of Python2.5 and fix py3 warnings

setup.py

@@ -53,7 +53,6 @@ setup(name='trytond_currency',
         'Natural Language :: Russian',
         'Natural Language :: Spanish',
         'Operating System :: OS Independent',
-        'Programming Language :: Python :: 2.5',
         'Programming Language :: Python :: 2.6',
         'Programming Language :: Python :: 2.7',
         'Topic :: Office/Business',

tests/test_currency.py

@@ -1,7 +1,6 @@
 #!/usr/bin/env python
 #This file is part of Tryton.  The COPYRIGHT file at the top level of
 #this repository contains the full copyright notices and license terms.
-from __future__ import with_statement
 import sys, os
 DIR = os.path.abspath(os.path.normpath(os.path.join(__file__,
     '..', '..', '..', '..', '..', 'trytond')))