This also forces the result of operations to be considered purely as
8-bit results in _some_ cases, but not in others. We were missing some
times when an overflow is the expected behavior; because SET_RESULT()
and mos6502_modify_status() use ints, this overflow was not properly
observed.
Regarding soft switches, we had several we should have been listening
for on both reads and writes, but were only doing so on writes; this is
now fixed.
Regarding statuses, we were incorrectly calculating both carry and
overflow. This should now be fixed, although some quick examinations of
disassembly output suggest there is something else amiss. Debugging will
continue shortly.
