Adds Py2.5 to Travis, and use Tox

.travis.yml

@@ -1,6 +1,7 @@
 language: python
 python:
+    - 2.5
     - 2.6
     - 2.7
-install: pip install -r requirements/default.txt -r requirements/test.txt
+install: pip install --use-mirrors tox
-script: nosetests
+script: TOXENV=py$(echo $TRAVIS_PYTHON_VERSION | tr -d .) tox