twisted.protocols.test.test_tls fails when SSL is not available

New submission from azverkan <None>:

This test failure was encountered with win32 Python 2.6

[ERROR]: twisted.protocols.test.test_tls

Traceback (most recent call last):
  File "c:\work\twisted\twisted\trial\runner.py", line 640, in loadByNames
    things.append(self.findByName(name))
  File "c:\work\twisted\twisted\trial\runner.py", line 450, in findByName
    return reflect.namedAny(name)
  File "c:\work\twisted\twisted\python\reflect.py", line 462, in namedAny
    topLevelPackage = _importAndCheckStack(trialname)
  File "c:\work\twisted\twisted\protocols\test\test_tls.py", line 24, in <module>
    from twisted.internet.ssl import ClientContextFactory, PrivateCertificate
  File "c:\work\twisted\twisted\internet\ssl.py", line 46, in <module>
    from OpenSSL import SSL
exceptions.ImportError: No module named OpenSSL

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Type     : defect
Component: core
Keywords : 
Priority : normal
Nosy     : 
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http://twistedmatrix.com/trac/ticket/3852