Truncating history (Re: Sparse clones)

> Fake-roots are special refs that declare certain commit objects
> as root-commits). Each time git walks down the history, it checks
> whether the current commit is an fake-root and so treats it as
> having no ancestor. That should be generic enough let everything
> else (commit, push, gc, etc) work as usual.
> 
> The only tricky point is when to update remote fake-roots: the
> remote should not cut off my local repo (unless explicitly asked).
> So remote fake-roots should only be imported if the local/receiving
> side has not the dropped commits anymore.