Commit annotations (was:: Octopus merge: unique (?) to git, but is it useful?)

> One of the things I could imagine using git for is to have "annotation 
> branches" for things like code review etc. They'd be a real branch in 
> their own right and with their own history, but at the same time they 
> could well want to point back to the "code branch" that they annotate by 
> considering that another parent in a "non-data merge" (and yes, you'd 
> obviously have to use a special merge strategy for things like that, but 
> you'd likely integrate it in some "annotation tool chain" rather than 
> anything else).