Add frame control code to display class, try to keep
VBA running at 60 FPS smoothly.
(1) When CPU core speed less than 95% I drop frames,
and when CPU core speed more than 105% I increase
frames to render.
(2) At the end of frame rendering, I sleep a short period of
time if the emulator is running too fast.
The result is quite acceptable, no matter use hq2x filter
or no filter, the emulator can adjust to keep almost 100%
CPU speeds to run.
*NOTE* This patch is for the code on CVS at 07/21/2005