Reworked IoMonitor to work with poll(2) instead of select(2).

The poll(2) syscall is more modern than select(2).
While performance impact increases linearly with the number
of connections, the overhead will be insignificiant up to a
few thousand connections. The good think about poll(2) is
simplicity and general availability on all mordern POSIX systems.

Signed-off-by: Frank Mertens <frank@cyblogic.de>
House keeping.

Signed-off-by: Frank Mertens <frank@cyblogic.de>