[NTVDM]

[NTVDM]
- Modify the int32 dispatch to clear the CF only on entry, so that we can
track in our handlers whether it was the first time the BOP executed.
- Implement INT 15h, AH = 41h (Wait On External Event).
- Fix INT 15h, AX = E801h - modify the stack CF instead of the handler CF.
- Make INT 16h AH = 00h clear CF when there is a character, so that the BOP doesn't
repeat.

svn path=/trunk/; revision=67612