Attempt to use python 2.4 when running tests wiht tox.

tox.ini

 [tox]
 envlist =
-    py25, py26, py27, pypy, py25-trunk, py26-trunk, py27-trunk, pypy-trunk, docs
+    py24, py25, py26, py27, pypy, py24-trunk, py25-trunk, py26-trunk, py27-trunk, pypy-trunk, docs
 [testenv]
 commands =
     python setup.py test
@@ -10,6 +10,11 @@ deps =
 
 # We lied here, these are not really trunk, but rather the 1.3 alpha-1, which
 # is close enough.
+[testenv:py24-trunk]
+basepython = python2.4
+deps =
+    http://www.djangoproject.com/download/1.3-alpha-1/tarball/
+
 [testenv:py25-trunk]
 basepython = python2.5
 deps =