This fixes the test on Mac OS X and SmartOS (probably other Solarises).
Also updates the sockets using ipc: to use DEALER sockets instead
of PAIR sockets.

Add explicit check for primary group.

Adds ZMQ_IPC_ACCEPT_FILTER_{PID,UID,GID} socket options to add processs,
user, and group IDs to the IPC filter sets. Fixes LIBZMQ-568.