- Change to use non blocking read to empty channel in case of too large sd number
 - Don't check for too large socket number on Windows.


sql/net_serv.cc:
  Windows does not need protection from sd >= FD_SETSIZE, it uses an array to store the sd's it should read from.
  Change the handler for when "net_data_is_ready" returns -1 to perform nonblocking read to empty the net.
  Only include that handler if HAVE_POLL is not defined  and not windows