[NTVDM]

[NTVDM]
- Start to refactor the DOS sources:
  Introduce the DEM (DOS Emulation) support library that is used by our built-in DOS, and that is used (via BOPs) by windows NT DOS (files: ntio.sys and ntdos.sys).
- Export some of DEM functions; stub most of them and implement the remaining ones (with existing code that we had in dos.c before).

svn path=/branches/ntvdm/; revision=61838