previous tb-set-node-routertype, and replace with a global directive
that sets the router for the entire NS file (all nodes). Also change
from "gated" to "ospf". New command is:

	tb-set-ip-routing "none|ospf"

	tb-set-node-routertype $node none|gated

Added slots to virt_nodes and nodes table. This stuff is carried
through so that tmcd can get at it and pass it back to client.

Complete rewrite.  Includes a great deal more documentation including a
description of IP allocation.  Also uses the new format.

Note: The section on tb-create-os is unfinished.  I need some info from
Leigh, then I'll fix it up.

tb_compat.tcl

The NOP version of tb_compat.tcl that users should download to run their
scripts with NS.  There is a link to this file in nscommands.html.

postparse now uses tbcmds
sim.tcl is updated to close (and flush) the tbcmds output stream if it
exists.
tb_compat.tcl is the TB version that should be included by newstyle ns scripts.
tb_compat_nop.tcl is the NS version that should be renamed to tb_compat.tcl
and included by scripts when they are run under ns.  I.e. scripts
	source tb_compat.tcl
as the first line and then use either the TB or the NS (nop) version depending
on what they are doing.