General overview of the facilities of the DGD Networking package

This package extends the IP networking features of DGD, at the cost of some
security.  (A driver that can initiate connections or send udp packets can,
if its internal security fails, be used as a platform for further attacks
by a cracker or other malicious user.)

Note: Like the file access functions, the network functions are
unprotected.  If you install this package, you must redefine the functions
connect() and open_port() in the auto object to implement the desired
security.  A common method is to allow any object in /sys/net/ (and no
others) to call these functions.

The networking package introduces three special kinds of objects:
	- tcp and telnet port objects
	- tcp and telnet connection objects
	- udp port objects

Tcp and telnet port objects are associated with a tcp port.
Whenever a client seeks a connection with a port DGD has opened, 
	connection(string clienthost, int clientport)
is called in the port object associated with that port.  This function is
expected to return an object that will function as the connection object
for that client.

Udp port objects are associated with a udp port.  There are no udp
connection objects.  When a udp datagram arrives on a port DGD has opened,
	receive_datagram(string data, string fromhost, int fromport)
is called in the udp port object associated with it.

Tcp and telnet connection objects are associated with a client.  Whenever
data arrives on a tcp connection, receive_message(string data) is called in
the connection object.  When data arrives on a telnet connection, the
driver parses it according to the telnet protocol.  Whenever a full line is
parsed, receive_message(string text) is called in the connection object.

See the Introduction text for a more complete explanation of what functions
are called, when they are called, and what they mean.

There are kfuns for opening ports, sending udp datagrams and tcp/telnet
data, and initiating tcp or telnet connections. See kfun/open_port,
kfun/send_datagram, kfun/send_message, and kfun/connect.

The config-file entries `telnet_port' and `binary_port' are still valid but
will be ignored.  The driver object should take care of opening the
appropriate ports during initialization.

The kfun users() returns all connection objects.  The kfun ports() returns
all port objects.  The kfun query_ip_number() returns 0 for port objects.
The config-file entry `users' also counts port objects.

The driver-object functions telnet_connect() and binary_connect() are
no longer used.

Acknowledgements:
I would like to thank Robert Leslie, Erwin Harte, and Adam David for
their willingness to run real projects on test versions of this package,
for many excellent suggestions, and for their help in hunting down and
killing some nasty bugs.

Richard Braakman <dark@xs4all.nl>