Log Message: 
Allow specification of values for multiple variables a once for
eval(), substitute() and so on. You can use
$f>eval(['x','y'] => Point(1,2));
or
$f>eval(['x','y'] => [1,2]);
or
$P = Point(1,2);
$f>eval(['x','y'] => $P);
to do the equivalent of
$f>eval(x=>1,y=>2);
Note that you must use quotes for the variable names and that they
must be enclosed in square brackets, not parentheses, when you supply
more than one variable. You can combine single with multiple
variables, as in
$f>eval(['x','y']=>Point(1,2),z=>3);
