Add a polling loop in main to read from more than one socket at once. Add the O_NONBL...

Add a polling loop in main to read from more than one socket at once. Add the O_NONBLOCK and
SO_KEEPALIVE flag to all sockets. Note that several loops which used to continue on a return value
of 0 (theoretical since 0 would never be returned without O_NONBLOCK) now break on 0 so that they
won't continue reading until after poll is called again.