Can't checkout branch name if a commit starts with the branch name

[BinaryMuse]

e.g. with a branch named b2 and a commit named b2a13fc, git checkout b2 will check out the commit

[BinaryMuse]

I think for our demo if b2 uniquely identifies a commit but cannot identify a commit vs. a branch (i.e. there is a branch named b2), we could say "'b2' could refer to the commit or to the branch 'b2'. Defaulting to ; if you want the branch, use 'refs/heads/b2'." We just need to implement refspecs that use refs/heads/....