all of twisted.test.test_twistd is erroneously skipped

[exarkun]

On NixOS:

[SKIPPED]                                                                                                                                                                                                                                                 
twistd unix support not available                                                                                                                                                                                                                         
                                                                                                                                                                                                                                                          
twisted.test.test_twistd.DaemonizeTests.test_error
twisted.test.test_twistd.DaemonizeTests.test_errorInParent
twisted.test.test_twistd.DaemonizeTests.test_errorInParentWithTruncatedUnicode
twisted.test.test_twistd.DaemonizeTests.test_errorMessageTruncated
twisted.test.test_twistd.DaemonizeTests.test_hooksCalled
twisted.test.test_twistd.DaemonizeTests.test_hooksNotCalled
twisted.test.test_twistd.DaemonizeTests.test_nonASCIIErrorInParent                                 
twisted.test.test_twistd.DaemonizeTests.test_success                                                                         
twisted.test.test_twistd.DaemonizeTests.test_successEINTR                                                                                                                                                                                                 
twisted.test.test_twistd.DaemonizeTests.test_successInParent                                                                                                                                                                                              
twisted.test.test_twistd.DaemonizeTests.test_successInParentEINTR                                                                                                                                                                                         
twisted.test.test_twistd.DaemonizeTests.test_unicodeError                                                                                                                                                                                                 
twisted.test.test_twistd.DaemonizeTests.test_unicodeErrorMessageTruncated                                                    

[exarkun]

This is due to 78cb734 in which a requirement for the modules "twistd.scripts._twistd_unix" and "twistd.python.syslog" was added for this module to run.