just use python 2.7 as dependency not to require unittest2 backport

--- circus-0.6.0/circus/tests/support.py~	2012-12-17 10:32:38.000000000 +0200
+++ circus-0.6.0/circus/tests/support.py	2013-03-09 14:53:09.604127893 +0200
@@ -6,7 +6,7 @@
 import cProfile
 import pstats
 
-import unittest2 as unittest
+import unittest
 
 from circus import get_arbiter
 from circus.util import DEFAULT_ENDPOINT_STATS
--- circus-0.6.0/setup.py~	2012-11-20 13:23:11.000000000 +0200
+++ circus-0.6.0/setup.py	2013-03-09 14:54:31.667912200 +0200
@@ -40,7 +40,7 @@
           "License :: OSI Approved :: Apache Software License",
           "Development Status :: 3 - Alpha"],
       install_requires=install_requires,
-      tests_require=['webtest', 'unittest2'],
+      tests_require=['webtest'],
       test_suite='circus.tests',
       entry_points="""
       [console_scripts]