Refactor the handshake code from first principles to remove code that was borrowed...

Refactor the handshake code from first principles to remove code that was borrowed from Netty, which is released under an incompatible license (Apache v2.)  Since our SSLEngineManager class was loosely inspired by, but no code was actually borrowed from, the Oracle JSSE examples, it is my opinion that it was incorrect to attribute copyright to Oracle, so that message has been removed (their examples are released under a BSD-style license, anyhow, so it's a non-issue.)

git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@4962 3789f03b-4d11-0410-bbf8-ca57d06f2519