Apply a gentler --force

[BobKerns]

Right now, the sanity checks are all-or-nothing. However, there's one documented use case that forces the use of --force, which is obviously not desirable.

To truncate history we need to do 'git replace --graft new_root'. This leaves the repo in an "unpacked" state. (We also need to remove references that do not have our new root as ancestor, e.g.:

git for-each-ref --no-contains=$FIRST --format='%(refname)' | xargs -n 1 git update-ref -d

)

Rather than bypass all checks, it would be better to have a flag that accepts new update refs and an unpacked state.

Alternatively, the documentation could suggest doing:

git pack-refs
git gc --prune=now

and then supplying a suitable value for --replace-refs (so there are arguments)