testExpandUser fails on cygwin

[ffigiel]

When running python fake_filesystem_test.py on cygwin x86_64 (On windows 8.1), testExpandUser fails.

Output:

FAIL: testExpandUser (__main__.FakePathModuleTest)
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Traceback (most recent call last):
  File "fake_filesystem_test.py", line 1858, in testExpandUser
    self.assertEqual('/root', self.path.expanduser('~root'))
AssertionError: '/root' != '~root'

After changing
1852 if sys.platform.startswith('win'): to:
1852 if sys.platform.startswith('win') or sys.platform == 'cygwin':,
the output is now:

FAIL: testExpandUser (__main__.FakePathModuleTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "fake_filesystem_test.py", line 1854, in testExpandUser
    self.os.environ['USERPROFILE'].replace('\\', '/'))
AssertionError: '/home/Filip' != 'C:/Users/Filip'