first version of the zeroconf lib

allows browsing (detection) of services using dns-sd, i.e.
DNS Service Discovery, or Bonjour see http://www.zeroconf.org/
The exposed interface is reentrant and threadsafe

Change-Id: I957d69696aa3c8ad625e074389b649b00b9153cf
Reviewed-on: http://codereview.qt-project.org/5410


Reviewed-by: Fawzi Mohamed <fawzi.mohamed@nokia.com>
Sanity-Review: Qt Sanity Bot <qt_sanity_bot@ovi.com>