. Specifically IBIZA.DSK demo which streams data from the disk throughout (ie. so runs at full-speed all the time)
. Update the screen every frame, but only if video memory has changed (check AZTEC.DSK loading time)
. NB. When running at full-speed, then 6502 emulation doesn't do cycle-accurate video updates
Fixed crash that could occur when switch video mode (F9) when running at full-speed
. Occured when g_nVideoClockVert was >= 192
Fixed JoyUpdateButtonLatch() to debounce in 5mecs instead of 5secs!
SpkrToggle() was using redundant global ('cyclenum') when using the PC speaker.
. I reworked the code (as it looked out-of-date),
but probably better to just remove all the PC speaker support.
- allowed some simplification to VideoSetMode()
Tidy up ContinueExecution(), removing unused 'BOOL pageflipping'.
Refactor VideoCheckPage() to make it more readable.
