darcs convert takes four options that are actually rather sub-commands
than options: --import, --export, --darcs-1, and --darcs-2, where the
last one serves as the default.
It might be a good idea to make this clearer to the user by turning
convert into a super command with four sub-commands.
See also issue2394.
The following patch sent by Guillaume Hoffmann <email@example.com> updated issue issue2396 with
* resolve issue2396: make convert a supercommand and enhance help strings