Add py27 to tox

tox.ini

 [tox]
 downloadcache = {toxworkdir}/cache/
-envlist = python2.6-django1.5,python2.6-django1.4,python2.6-django1.3
+envlist = py2.7-django1.5,py2.7-django1.4,py2.7-django1.3,py2.6-django1.5,py2.6-django1.4,py2.6-django1.3
 
 [testenv]
 commands = {envpython} rest_framework/runtests/runtests.py
 
-[testenv:python2.6-django1.5]
+[testenv:py2.7-django1.5]
+basepython = python2.7
+deps = https://github.com/django/django/zipball/master
+
+[testenv:py2.7-django1.4]
+basepython = python2.7
+deps = django>=1.4.1
+
+[testenv:py2.7-django1.3]
+basepython = python2.7
+deps = django>=1.3.2
+
+[testenv:py2.6-django1.5]
 basepython = python2.6
 deps = https://github.com/django/django/zipball/master
 
-[testenv:python2.6-django1.4]
+[testenv:py2.6-django1.4]
 basepython = python2.6
-deps = django>=1.4,<1.5
+deps = django>=1.4.1
 
-[testenv:python2.6-django1.3]
+[testenv:py2.6-django1.3]
 basepython = python2.6
-deps = django>=1.3,<1.4
+deps = django>=1.3.2