Finally fixed problems with demo mode.

Finally fixed problems with demo mode.

Turns out the v6809 code didn't take indexed mode memory access timing
into account, and so the emulated CPU ran ahead of what it would
normally do.  Also added PIA emulation, as it seems the IRQ system that
the CPU utilizes is active low.  There's still a bit more to do
vis-a-vis the v6808 & v6809 cores in that SYNC and CWAI don't work
properly and the v6808 core clears its own IRQ/RESET lines (which, it
can't do in real life).  So there's a wee bit more to clean up, but not
much.  :-)