[NTVDM]

[NTVDM]
- Move almost all the DOS command launch thread into dem.c,
- Rework the code so that now, when we want to either load our BIOS32 or a custom one, we start their execution at F000:FFF0 as it should be,
- For modularity purposes (ie. to be able one day to load real OSes in our ntvdm), implement INT 19h (bootstrap loader) so that it calls a (temporary) dos bootsector loader that writes some bootstrap code at 0000:7c00, then the INT 19h runs this code, that has as an effect to load our DOS32 (for a real OS, the MBR code goes to 0000:7c00 and is then run).

svn path=/trunk/; revision=64521