Keep +2 reviews valid even if new patch set is pushed

You often have reviews like 'patch is okay, but maybe fix the typo in the commit message?'. That is, I'd like to give the general commit an okay, but the original author might consider to fix a few small things. I trust the committer enough to decide for himself though to do these, and don't want to be bothered to do yet another review.

Gerrit right now requires a final review for the very last patch-set committed. It could also keep a +2 as a valid review for the whole patch, even if a new patch-set is added afterwards.