Finally fix Python 2.6.

Also added a syntax for 2.6. There are some thing that just don't work in 2.6.

conftest.py

@@ -152,6 +152,12 @@ def works_in_py2(each_version):
     return Checker(each_version, each_version.startswith('2'))
 
 
+@pytest.fixture
+def works_ge_py27(each_version):
+    version_info = parse_version_string(each_version)
+    return Checker(each_version, version_info >= (2, 7))
+
+
 @pytest.fixture
 def works_ge_py3(each_version):
     version_info = parse_version_string(each_version)