* For the direct modes, get rid of the predefined palettes and use the
system's EGA palette instead (like planar modes do). Since palette
values can be 5:5:5, 5:6:5, 8:8:8 etc., add code to refresh them via
the adapter's palette registers upon video mode change. Scrap the
ugly vga_drawpxl() macro. This makes 15 and 16 bit modes faster than
24 or 32 bpp.
* Fix mouse pointer drawing code for direct modes. Never draw the
pointer in the border area so that direct and planar modes can now
share a single function for removing the mouse.
* Do some minor cleanup and restructuring.