Implement thread name on windows, cleanup thread naming internals

src/io_thread.cpp

@@ -57,10 +57,8 @@ zmq::io_thread_t::~io_thread_t ()
 void zmq::io_thread_t::start ()
 {
     char name[16] = "";
-#ifndef ZMQ_HAVE_WINDOWS
     snprintf (name, sizeof (name), "IO/%u",
               get_tid () - zmq::ctx_t::reaper_tid - 1);
-#endif
     //  Start the underlying I/O thread.
     _poller->start (name);
 }