The return value now better reflects what has happened:
1 on success (incoming connection on listen socket, we
accepted it successfully), -1 on error, 0 on timeout.

Also change the select calls to not check _all_ possible
file descriptors.
Signed-off-by: Christian Beier <dontmind@freeshell.org>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>