Log Message:
Update py-twisted to 16.4.1.

Twisted Core 16.4.1 (2016-09-07)
================================

Features
--------
 - Client and server TLS connections made via the client TLS endpoint
   and the server SSL endpoint, as well as any other code that uses
   twisted.internet.ssl.CertificateOptions, now support ChaCha20
   ciphers when available from the OpenSSL on the system. (#8760)

Bugfixes
--------
 - Client and server TLS connections made via the client TLS endpoint
   and the server SSL endpoint, as well as any other code that uses
   twisted.internet.ssl.CertificateOptions, no longer accept 3DES-
   based cipher suites by default, to defend against SWEET32. (#8781)