Fixed socket options to track latest libzmq master

- Added various missing options
- Only selftest CURVE options if libsodium is available
Using proper test keys for CURVE
Trivial name change
Fixed use of ZMQ_STREAM to work with older libzmq

- defines ZMQ_STREAM if it's not defined
- if older libzmq apps try to use ZMQ_STREAM it will assert in libzmq
Merge pull request #204 from hintjens/master

CZMQ doesn't build with libzmq 3.2.3 stable
Minor cleanup of variable name
Merge pull request #205 from hintjens/master

Minor cleanup of variable name