Add socket option "ZMQ_ROUTER_HANDOVER" (ZMQ 4.1)

[ggtaylor]

Reference: http://api.zeromq.org/4-1:zmq-setsockopt#toc24

[kkoopa]

There's a 4.1 now? Add that to .travis.yml so it gets tested against, and please provide a test case of the functionality conditional on this version of libzmq.

[ggtaylor]

There is no official release for 4.1 yet, but this option is in the 4.1 API (http://api.zeromq.org/4-1:zmq-setsockopt#toc24) and in the libzmq trunk.

I don't want to add the libzmq trunk env to .travis.yml, but this option hasn't been branched yet. Should I wait until it's branched?

[kkoopa]

You're right about not wanting to test against trunk, but tests will still be needed at some point. Let's see what @ronkorving has to say. From what I've seen in libzmq in the past, things can get renamed, removed and introduced even as late as in beta releases. They can also be buggy.

[ronkorving]

I think it makes sense to wait until this feature is actually versioned. Until that time, if you really need this, I think it's better if you work off your own branch. I'll keep this PR open so you can update it when 4.1 is out.

[mmhmmh]

ZMQ 4.1.2 stable is out. It would be nice if this option can be merged to master as it is necessary when identity is reused. Otherwise, the router socket will silently ignore the new connection with the duplicated identity.

[ronkorving]

I'm all for supporting more options, and it seems the time is right for this one :) A rebase + making TravisCI happy would be in order though.