fake_filesystem_unittest.py uses python2 __builtin__

[user150512]

I have crash as follows

    [...]tests/__init__.py", line 17, in setUp
        self.setUpPyfakefs()
      File "/usr/local/lib/python3.4/dist-packages/pyfakefs-2.4-py3.4.egg/fake_filesystem_unittest.py", line 87, in setUpPyfakefs
        self._stubber.setUp()
      File "/usr/local/lib/python3.4/dist-packages/pyfakefs-2.4-py3.4.egg/fake_filesystem_unittest.py", line 201, in setUp
        startPatch(self, '__builtin__.file', self.fake_open)
      File "/usr/local/lib/python3.4/dist-packages/pyfakefs-2.4-py3.4.egg/fake_filesystem_unittest.py", line 198, in startPatch
        print("Warning: Could not patch '{}' on module '{}' because '{}' resolves to {}".format(attribute, target, target, patch.getter()))
      File "/usr/local/lib/python3.4/dist-packages/mock.py", line 1414, in <lambda>
        getter = lambda: _importer(target)
      File "/usr/local/lib/python3.4/dist-packages/mock.py", line 1098, in _importer
        thing = __import__(import_path)
    nose.proxy.ImportError: No module named '__builtin__'

In Line 201 of fake_filesystem_unittest.py

    startPatch(self, '__builtin__.file', self.fake_open)

the old name __builtin__ is used instead of python3 version builtins.

In mock.py as included in Traceback you can find the line

builtin = '__builtin__'
if inPy3k:
    builtin = 'builtins'

[user150512]

        builtin = '__builtin__'
        if (sys.version_info[0] == 3):
            builtin='builtins'

        startPatch(self, builtin + '.file', self.fake_open)
        startPatch(self, builtin + '.open', self.fake_open)

in fake_filesystem_unittest.py yields to error:

Warning: Could not patch 'file' on module 'builtins' because 'builtins' resolves to <module 'builtins' (built-in)>
         See mock module bug 250, https://code.google.com/p/mock/issues/detail?id=250

[jmcgeheeiv]

In issue #48 I propose a solution to this issue.

[jmcgeheeiv]

I switched pyfakefs from mock to mox3, so this issue should be resolved.