Some of the old patches had missing objects and that causes problems
during the ref advertisement, as the object is not found.
In this patch, we check that the object exists and also that the patch
is still open. Otherwise a remote tracking branch is created for every
single patch ref.
This adds the ability to the git-remote-helper to open and update
patches via a `git push` to the magic ref `refs/patches` and
`refs/heads/patches/<patch-id>`.
The main change is that we had to move away from offering the `connect`
capability in the remote helper, to offering `push` and `fetch`
individually.
To get a feel for how this works, see the `rad-patch-via-push.md`
example.
Alexis Sellier
cloudhead