Add configuration for tox.

tox.ini

@@ -0,0 +1,20 @@
+[tox]
+downloadcache = {toxworkdir}/cache/
+envlist = py27, pypy
+
+[testenv]
+deps =
+    unittest2
+
+commands = make check
+recreate = True
+whitelist_externals = make
+
+[testenv:py24]
+setenv =
+    PIP_INSECURE=1
+
+
+[testenv:py25]
+setenv =
+    PIP_INSECURE=1