originally anticipated, but I was worried about confusion with the
Agent/Application API that NS provides, and which is substantially
different than this. Anyway, I added support for this syntax:

	set prog0 [$ns program]
	$prog0 set node $nodeA
	$prog0 set command "/bin/ls -lt >& /users/stoller/logs/foo"

Kinda obvious, although whats not obvious is that without events to
start and stop them, these will never run. So, I added support for
this:

	$ns at 10 "$prog0 start"
	$ns at 20 "$prog0 stop"

You can start and stop programs as much as you like, but you cannot
start a program that is already running; you have to stop it first.
You can also issue these dynamically using the same api:

	tevc -e testbed/Tevents now prog0 start \
		"command=/bin/ls -lt / >& /users/stoller/logs/foo"
	tevc -e testbed/Tevents now prog0 stop

Note the quotes when using a multiword command. I also had intened to
support a KILL command so that you could send arbitrary signals to a
process. I added that, but I will not bother to document it yet; since
I invoke /bin/csh to process the command line, the issue of signals is
a little fuzzy. Sending a signal like -HUP to the parent process (the
csh) is not really what we want to do. I think we can support this,
but I need to poke around and see what the right way is.