#1 freeze on /0

[Noah Roberts]

When trying to graph things like rational expressions
where some values of X could be a divide by 0 qplot
freezes. qplot should discover what could be 0, when
looking for domain of func, and avoid it.

the bc that is in qplot correctly deals with div by 0,
pukes and error and continues to function. Perhaps
qplot should be more tollerant of erroneous input from
the bc pipe.

thanks
NR