The standard netcat, while ubiquitous, doesn't handle broadcast udp packets
properly.  The local ncb util does however.  So if ncb can be located in
the standard locations, automatically use that instead.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

The netcat utility likes to exit when it receives an empty packet (as it
thinks this means EOF).  This can easily occur when working with command
line editing as this behavior will be triggered when using backspace.  Or
with tabs and command line completion.  So create two netcat processes -
one to only listen (and put it into a loop), and one to do the sending.
Once the user quits the transmitting netcat, the listening one will be
killed automatically.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

While the doc/README.NetConsole does have a snippet for people to
create their own netcat script, it's a lot easier to make a simple
dedicated script and tell people to use it.

Also spruce it up a bit to make it user friendly.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>