suggestion for a simple addition: git update-ref --ff-only

Hi list,

I'd like to suggest a very simple, but IMHO quite useful, additional option to git-update-ref: an option --ff-only which would cause the command to refuse unless the current ref is an ancestor of the new one.

The reason I think it would be useful: I occasionally wish to perform a trivial (i.e., fast-forward) merge of some branch into another (e.g., after a git-fetch) without checking it out. Now git-update-ref is perfect for that, but there is always the possibility of getting something wrong (which one would not have with git merge --ff-only, but the latter requires checking out the branch), and this option would avoid tedious verifications.

Happy hacking,