Using '-r null' instead of '-v' as the overriden command default.
The latter did not have any effect on output, thus not giving much
indication on whether the modified defaults were really in use or not.
- hg archive --no-decode has no short option, too, and maybe both could use
-d in the future to select revisions by date.
- opts.get makes python scripts calling cat() happy, because they don't have
to pass the new option.
