non fast forward updates

[Hleb Valoshka <375gnu@gmail.com>]

Hello!

I decided to help rails packagers and update ruby-sprockets to fix
#725386. But I didn't noticed problems with branches `upstream' and
`pristin-tar' until I did `git push'. So now ruby-sprockets repository
requires `git rebase -i' (and ruby-atomic requires it too, but it
doesn't in so ugly state).

So, I'm sorry, but is it possible to enable non fast forward updates
temporary with that repos or to rename them and create empty repos
where I can push cleaned up commits?