Update Csocket to 7c9c6ef676818457a952c2bda478ce7e27a928bf

* Add encoding mode which reads UTF-8 and something else, but sends UTF-8
* Expose encoding conversion error callbacks to subclasses
Webadmin: Add GUI for character encoding
Don't break IRC control characters in some encodings

Fix #577
sasl.cpp: don't advertise DH-* as secure

They were removed from Atheme, because people thought them to be more
secure than PLAIN + SSL, so ZNC shouldn't advertise them as secure.

I think that DH-AES and DH-BLOWFISH should say something about not being
widely supported, but I am not sure what. Newer Atheme doesn't support
it and with Anope they are optional unlike PLAIN and EXTERNAL that are
in their SASL core.
Merge pull request #779 from Mkaysi/sasl

sasl.cpp: don't advertise DH-* as secure