Merge pull request #531 from hintjens/master

Added GSSAPI socket options
Merge pull request #533 from hintjens/master

Problem: CZMQ always catches SIGINT / SIGTERM
Merge pull request #534 from hintjens/master

Problem: zctx_new always catching interrupt signals
zsys: don't leak string when realloc fails

We are not interested in realloc since the string is rewritten
in full anyway.  Switch to a more explicit free/malloc style.
Merge pull request #535 from fichtner/realloc_leak

zsys: don't leak string when realloc fails
Merge pull request #536 from hintjens/master

Problem: selftest failing on libzmq 4.0.x without libsodium
Problem: gossip protocol was not broadcasting changes

Due to bug in zproto server engine that was not broadcasting events
properly. Fixed in zproto, engine regenerated here.

Also expanded test case in test_zgossip.c.
Added versioning to zgossip protocol