FAST FORWARD PLAYBACK

Fast-forward playback is protected against a bufferfill deadlock.
Use it like this: 

  extern sidEmuFastForwardReplay(int samplesPercentage);

Where the parameter is out of [1=fastest,...,100=normal_speed].
Examples:

  50 = 2x faster
  25 = 4x faster
  12 ~= 8x faster
  3 ~= 32x faster

Playback speed is increased by calculating fewer samples per C64 player call.
To fill the sample buffer more C64 player calls have to be done. Hence the
6510-interpreter usage increases. This might be too much for slower machines.

Alternatively, it would be possible to call the 6510-interpreter without
calculating any samples at all.