cache.py, fix python3.2 support
Masterbranch can pass all original tests on 1.5ver

This commit allows masterbranch to pass all original tests with Django 1.5 (python2).

Django 1.5 introduce python's bultins vars "True", "False", "None" to the Context, as part of  BaseContext class:

"""
class BaseContext(object):
    def __init__(self, dict_=None):
        self._reset_dicts(dict_)

    def _reset_dicts(self, value=None):
        builtins = {'True': True, 'False': False, 'None': None}
        if value:
            builtins.update(value)
        self.dicts = [builtins]
"""
https://github.com/django/django/commit/93240b7d903af86e135c3b1724a81d2daf31441f

So, now we always have List's first element that contains these vars.

Should we see this in the django-debug-toolbar?
Update .travis.yml

don't allow failures