The compression is done in two stages:
1) The signals are compressed using KisSignalCompressor with a period
   of 10 ms. This effectively limits the frame rate by 100fps.
2) On some (slow) systems 100 fps might be too much, so before delivering
   the signal to the openGL canvas it is now checked whether the pipeline
   has already finished processing our previous update requests using
   KisOpenGLCanvas2::isBusy(). If the pipeline is still congested, we just
   resend the signal back to KisSignalCompressor.