This fixes the really odd bug of certain string values getting swapped
in vkgen when DEBUG_QF_MEMORY was defined in expr.c. It will also
prevent a lot of fun with floats in the future, I imagine.
This gets my `m * p * ~m` code as optimal as possible if my counting is
correct (this does not include the extra extends and add needed to merge
the values). Also, there might be a possibility of recombining some ops
into a vector op, but I'm happy with this.
That is, `x+x -> 2*x` (and similar for higher counts). Doesn't make much
difference for just 2, but it will make collecting scales easier and I
remember some testing showing that `2*x` is faster than `x+x` for
floating point.
Of course, motor-point keeps bouncing around numerically :/
