For now hardcode the path to brew version of openssl.

We require openssl 1.0.0 or later to build with the new crypto code.
Crypto code by Aldrin D'Souza under liberal 2-clause BSD license.

Credit where credit is due: taken from Aldrin's Notebook and a nice
accompanying article at http://aldrin.co/crypto-primitives.html
Remove migrated code.

It doesn't actually need a separate structure, but will need proper
padding applied where necessary.
Add boost::array<> constructor and fix tab indents.
Add DH init2 code.
Add picking chunks out of incoming message.
Our use of openssl requires -Wno-deprecated-declarations on OSX.
Use SSU packet signature in test.