Let's acknowledge everyone's contributions by replacing "Google LLC"
in the copyright header by "The Jujutsu Authors". If I understand
correctly, it won't have any legal effect, but maybe it still helps
reduce concerns from contributors (though I haven't heard any
concerns).
Google employees can read about Google's policy at
go/releasing/contributions#copyright.
It's annoying to have to add `--branch main` every time I push to
GitHub.
Maybe we should make it push only the current branch by default, but
we don't even have a concept of a current branch yet...
When there are two concurrent operations, we would resolve conflicting
updates of git refs quite arbitrarily before this change. This change
introduces a new `refs` module with a function for doing a 3-way merge
of ref targets. For example, if both sides moved a ref forward but by
different amounts, we pick the descendant-most target. If we can't
resolve it, we leave it as a conflict. That's fine to do for git refs
because they can be resolved by simply running `jj git refresh` to
import refs again (the underlying git repo is the source of truth).
As with the previous change, I'm doing this now because mostly because
it is a good stepping stone towards branch support (issue #21). We'll
soon use the same 3-way merging for updating the local branch
definition (once we add that) when a branch changes in the git repo or
on a remote.
