(cons x) yields no error message

[Moon at MIT-AI (David A. Moon)]

I have fixed this in the source by making OPTIMIZE check the number of arguments
in the case where the form is being replaced by the result of an optimizer.
There are still a number of functions which in the interpreter take an &REST
argument which is actually required to be at least one argument which this check
will not test; those functions already have checks in their optimizers for too
few arguments.