Install mock 1.0.1 on Python 2.6.

Fixes #1081

setup.py

@@ -45,7 +45,11 @@ with open(fname) as f:
     tests_require = [l.strip() for l in f.readlines()]
 
 if sys.version_info[:2] < (3, 3):
-    tests_require.append('mock')
+    # recent versions of mock doesn't support Python 2.6
+    if sys.version_info[:2] == (2, 6):
+        tests_require.append('mock==1.0.1')
+    else:
+        tests_require.append('mock')
 if sys.version_info[:2] < (2, 7):
     tests_require.append('unittest2')
 

tox.ini

@@ -7,6 +7,6 @@ usedevelop = True
 commands = py.test {posargs:tests/}
 deps =
   -rrequirements_test.txt
-  py26: unittest2
-  py2{6,7},pypy,py32,pypy3: mock
+  py26: unittest2, mock==1.0.1
+  py27,pypy,py32,pypy3: mock
   py3{3,4}: aiohttp