[Coco] Multi-pak interface and CART*

[Chuck Youse]

Does CART* only work for the selected slot?  I.e., if in a Coco 3, I
wanted to be able to generate an interrupt (either IRQ* or FIRQ*,
depending upon the GIME settings), is it possible?  Are there any
limitations (e.g., the slot must be selected)?

I don't have an MPI, but I'd like for this thing to work for folks who
have 'em, which is probably most ..

C.