Ok, zooko, do you think this recordget_race.sh script more or less reflects what
is going on? 

I get errors like 'Duplicate patch' and other darcs check failures.

It may be that the resolution for this is something that amounts to "tell the
user not to do that", but it depends on how realistic it is for this kind of
scenario to occur; if it happens with something like push/get, it would be big
trouble, I'm guessing.