Remove Python 2.6 support.

Fixes https://github.com/letsencrypt/letsencrypt/issues/515

.travis.yml

@@ -15,7 +15,6 @@ env:
   global:
     - GOPATH=/tmp/go
   matrix:
-    - TOXENV=py26 BOULDER_INTEGRATION=1
     - TOXENV=py27 BOULDER_INTEGRATION=1
     - TOXENV=py33
     - TOXENV=py34

setup.py

@@ -85,7 +85,6 @@ setup(
         'Operating System :: POSIX :: Linux',
         'Programming Language :: Python',
         'Programming Language :: Python :: 2',
-        'Programming Language :: Python :: 2.6',
         'Programming Language :: Python :: 2.7',
         'Topic :: Internet :: WWW/HTTP',
         'Topic :: Security',

tox.ini

@@ -6,7 +6,7 @@
 # acme and letsencrypt are not yet on pypi, so when Tox invokes
 # "install *.zip", it will not find deps
 skipsdist = true
-envlist = py26,py27,py33,py34,cover,lint
+envlist = py27,py33,py34,cover,lint
 
 [testenv]
 commands =
@@ -39,7 +39,6 @@ commands =
     ./tox.cover.sh
 
 [testenv:lint]
-# recent versions of pylint do not support Python 2.6 (#97, #187)
 basepython = python2.7
 # separating into multiple invocations disables cross package
 # duplicate code checking; if one of the commands fails, others will