Require ZMQ 3.0+, and fail when not provided.

[robertmaynard]

We should move to zmq 3.0 as a minimum version. The major benefit is that this will making using our own buffer classes easy.

[robertmaynard]

The superbuild has been updated to build zmq 3.2.4. Next up is to cause compile errors if we encounter zmq 2.X

[robertmaynard]

The superbuild has been updated to build zmq 4.1.2.