class type resolver = object .. end
method host_by_name : string -> Unixqueue.event_system -> Unix.host_entry engine
Look up the passed host name up. The implementation can be synchronous
        or asynchronous. In the first case, an engine is returned that is
        already in one of the states `Done he or `Error e where he is
        the host entry, or e is an exception like Host_not_found. In this
        case the passed event system is ignored. If the implementation is
        asynchronous, the caller must run the event system until the 
        state of the engine transitions to `Done he or `Error e.