[GEM Development] New VESA drivers

[John Elliott]

  I've updated the GEM/3 and GEM/4 video drivers again.

  Firstly, all the 256-colour drivers have been migrated to the new faster
bit-blit system.

  Secondly, I've modified the 256-colour driver source so it no longer 
requires the memory window size to be a multiple of the line length. This 
means that I can now support other modes than 1024x768x256. 

  Consequently, the driver packs have now been updated and include drivers
for VESA modes:

SDW649.VGA: 640x400 / 640x480
SDW869.VGA: 800x600
SDW109.VGA: 1024x768
SDW129.VGA: 1280x1024

 -- all in 256 colours.

 The old SD2569.VGA driver has been superseded by SDW109.VGA, and the old
SDV649.VGA has been renamed to SDW6X9.VGA (so that all 256-colour VESA 
drivers have names beginning SDW).

-- 
John Elliott