This fixes the problem that MMR1 is recording changes to R7 (PC), which it should not. (issue #44)

It does not fix the problem that MMR1 is not used for floating point instructions.

I don't know if I will fix the FP MMR1 problem. It does not seem to impact running software. It is consistent with the architecture spec - just not with the actual J11 implementation. The J11 microcode has a variety of exception exits for FP conditions, and I have to trace which ones invoke fix-up, and which do not.