setvbe command to set video mode

[Gerardo Richarte]

I have implemented a new grub command (setvbe) which can be used to 
switch the graphics mode before booting. It can take arguments like

   setvbe 1024x768x32 (scans the video modes for a suitable one) (*)
   setvbe 0x118 (set mode 0x118)

(*) it does not use the video mode list as used by vbeprobe because this 
method doesn't work on some systems, specially on qemu.

   It will add a command line option "video=" to the booted kernel, 
passing some arguments needed by the loaded kernel.

   I started using GRUB Legacy 0.97's source code for this, but now I'm 
using grub_for_dos 0.41 (0.42 did not work for me) which uses GRUB 
Legacy 0.97. I think the newer and more mantained version of GRUB Legacy 
is that one (grub 4 dos). Which includes lots of cool new features.

   If anybody's interested, I can send it personally or to the list.

   gera