Update to tox 1.6 and setup.py develop

Change-Id: Ie81f5ee5a8f7835f0600a4f4f46b25920d424e71

tox.ini

@@ -1,10 +1,17 @@
 [tox]
+minversion = 1.6
+skipsdist = True
 envlist = py26,py27,py33,pep8
 
 [testenv]
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
+install_command = pip install -U {opts} {packages}
+usedevelop = True
 setenv = VIRTUAL_ENV={envdir}
+         LANG=en_US.UTF-8
+         LANGUAGE=en_US:en
+         LC_ALL=C
          EVENTLET_NO_GREENDNS=yes
 commands =
    bash -x {toxinidir}/run-tests.sh {posargs}