MMD with native type right operand

[Leopold Toetsch]

I know, I've asked this question some time ago, and implemented
MMD_ADD_INT and friends. But I can't reproduce the full rationale WRT
dispatching of these methods.

add Px, Py, Iz

can clearly use only the left hand operand Py. So it's not a real MMD,
the right hand operand is always a plain integer. This would indicate
that it should be a vtable call.

OTOH

add Px, Py, Pz

is an MMD method. Having two different dispatch schemes seems a bit
undesirable for such similar operations. But two schemes are needed
anyway for overriding e.g. set_integer, which is a vtable.

So I'm quite unsure, what's right.

leo