Bump to 1.7.4
Updating ZMQ to v4.0.3
restore ruby signal handlers - don't need czmq ones
Fix verbose socket printing (null) instead of message.
Update ZMQ::Poller#poll to not raise exceptions on recoverable errors

EINTR and EAGAIN error codes are recoverable and can be handled in ruby code
Improve handling of strings will NUL characters in them