Add tox environments for python2.4-3.1

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist=du07,du06,du05
+envlist=py24,py25,py26,py27,py31,du07,du06,du05
 
 [testenv]
 deps=nose
@@ -7,11 +7,25 @@ commands=
     nosetests
     sphinx-build -W -b html -d {envtmpdir}/doctrees doc {envtmpdir}/html
 
+[testenv:py24]
+deps=
+    nose
+    simplejson
+
+[testenv:py31]
+deps=https://bitbucket.org/jpellerin/nose3/get/tip.zip
+
 [testenv:du05]
-deps=docutils==0.5
+deps=
+    nose
+    docutils==0.5
 
 [testenv:du06]
-deps=docutils==0.6
+deps=
+    nose
+    docutils==0.6
 
 [testenv:du07]
-deps=docutils==0.7
+deps=
+    nose
+    docutils==0.7