- 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.
Some systems show "Thu Jan 01" instead of "Thu Jan 1", which breaks tests.
Using "1000000" yields "Mon Jan 12 13:46:40 1970", which looks the same on
all systems.