[PATCH 0/6] MR6090: Cmd engine rewrite (part XXI)

[eric pouech (＠epo)]

This is part XX1 of cmd engine rewrite.

It covers:
- tests & fixes for success/failure of changing current drive,
- tests & fixes for success/failure when using pipes,
- new implementation of CHOICE command.

Notes:
- CHOICE is not a builtin command in native cmd.exe,
  but I kept it builtin for simplicity,
- CHOICE was (partially) implemented using syntax from
  MS-DOS days; it has been moved to use Windows' syntax.