Disallow failure of Python 2.6 builds again

The Python 2.6 build was allowed to fail, because it couldn't detect format
strings which use implicit parameters. It cannot just ignore P101-P103 results
as it'll also detect unused parameters (as P301) because it didn't detect that
it would be used on Python 2.7 and up.

So it just skips the tests which would usually fail.

.travis.yml

@@ -12,11 +12,6 @@ script:
   - python setup.py test
   - if [[ "$TRAVIS_PYTHON_VERSION" != "nightly" ]]; then coverage run setup.py test ; fi
 
-matrix:
-  allow_failures:
-    # Allow failures on 2.6 as it doesn't detect implicit parameters
-    - python: "2.6"
-
 notifications:
   email: false
 before_install:

test_flake8_string_format.py

@@ -9,7 +9,9 @@
 import sys
 import tempfile
 
-if sys.version_info < (2, 7):
+PY26 = sys.version_info[:2] == (2, 6)
+
+if PY26:
     import unittest2 as unittest
 else:
     import unittest
@@ -107,6 +109,7 @@ def run_code(self, code, positions, filename):
         checker = flake8_string_format.StringFormatChecker(tree, filename)
         self.run_test_pos(positions, self.create_iterator(checker))
 
+    @unittest.skipIf(PY26, 'Python 2.6 does not handle implicit parameters.')
     def test_checker(self):
         self.run_code(dynamic_code, dynamic_positions, 'fn')
 
@@ -218,6 +221,7 @@ def run_test(self, ignored='', is_ignored=lambda n: False):
         flake8_string_format.main(parameters + [self.tmp_file])
         self.run_test_pos(positions, self.iterator())
 
+    @unittest.skipIf(PY26, 'Python 2.6 does not handle implicit parameters.')
     def test_main(self):
         code = '#!/usr/bin/python\n# -*- coding: utf-8 -*-\n' + dynamic_code
         self.tmp_file = tempfile.mkstemp()[1]