Constant folding on fixnum->raw and raw->fixnum
Improve performance of make-varargs

By streamlining address handling.
Improve performance of apply

By streamlining address handling.
Simplify handling of box parameter variables

I've no idea why I made this so complicated.  We just need to box
up the parameter value.  There's no need to introduce synthetic variables.
Which are problematic because they leave hidden references in the original
parameter slots.