Better handling of EINTR in send_raw, receive_raw, receive(string),
and context::terminate. Also cause ~context to call terminate() which was
not previously occurring.

Also added reinterpret_casts to ensure the variadic message::add() method
was not called when the low-level void* overload was intended.
Merge branch 'develop' of https://github.com/zeromq/zmqpp into develop
Merge pull request #38 from LindleyF/develop

Develop