A safe "system" function



I'm working on integrating plotting into my web interface, and have  
been looking through plot.lisp a bit. I noticed that plot2d uses  
Maxima's "system" function (i.e. $system) to execute shell commands.  
However, I explicitly unbind $system in my init file and prevent  
execution of Lisp code to prevent users from executing malicious  
commands. This subsequently breaks plotting.

So I modified macsys.lisp and renamed $system to safe-system, and  
changed all references appropriately. I then wrote a new $system  
function, which just passes its arguments to safe-system. That way,  
Maxima can internally execute shell commands all it wants, while  
adding the ability to block users from doing the same.

Do you think this a worthy modification? Should it be committed, or  
will it break lots of other things?

Thanks,
-matt