This shaves off a good 800 KB from all the engines. However, do keep
local atari debug messages for diagnostic purposes.
Also, use natfeats for debug output when possible else the classic
stdout/stderr (not both as before).
- optimize fillScreen(): Eco Quest calls it way too often with 1x1 rects
- don't disable Cursor::isChanged() flags on !isVisible(), that leads to
skipping of _surface creation in some cases
- handle properly any number of parameters between beginGFXTransaction
and endGFXTransaction
- clear the work buffer when exiting a game to avoid showing it when
next game shows an error upon startup
Instead of having one globally in AtariGraphicsManager. This simplifies
code and cleans up a lot of dark corners in AtariGraphicsManager.
A slight disadvantage is that now the cursor surface has be to converted
for each buffer.