drop the rectangle fill workaround here as well

add *very* experimental Visualize FX support

Set S bit in IBOvals in NGLEPrepareCopy_EG() - without it we get garbage on the
right border. Don't seem to need it on HCRX.
While there, don't blindly assume 8bit colour when accessing off-screen memory.
Shouldn't make a difference now but we may eventually support 24bit devices that
have off-screen memory ( or figure out how to access it on HCRX )

comment cleanup, magic number reduction

add HCRX support

some cleanup:
- consistetly use buffer 0 - makes no difference when double buffering is
disabled ( which it should be ) but may bite us if it isn't
- add some comments on why we do what we do

add acceleration, Visualize EG only for now