ZVISION: screenSpaceToImageSpace return 0,0 when pointer outside working
window.
ZVISION: Don't need to set push flag in cursorDown because it's block
change cursor image.
ZVISION: Change platform detection of ZGI, dos->win.
ZVISION: Select needed workingWindow for ZGI and Nemesis.
ZVISION: Streamvideo alwayas skippable. Skippable flag renamed to
skipline.
ZVISION: Detach raw stream reader from RawZorkStream for creating
correct avi raw reader.