Use zeromq library C API, based on work by @wtfuzz and @hexwave. Fixes #1760.
Merge pull request #1612 from cmouse/use-zeromq-c-api

Use ZeroMQ C API
slightly improve docs of semantics of dynamic dns updates
Merge branch 'master' of github.com:PowerDNS/pdns
make sure we don't launch the query distribution thread if configured to run unthreaded
Merge branch 'secpoll' of github.com:ahupowerdns/pdns into secpoll
improve error message on reporting failed secpoll retrieval