The remote helper now supports the push option `patch.target`. This
allows users to explicitly specify a target canonical reference when
opening or updating a patch. For example, to open a patch that targets
the branch "backport", use:
```
git push -o patch.target=refs/heads/backport
```
Furthermore, strict merge and revert isolation is now enforced:
patches are only marked as merged or reverted if the commits are
pushed to the target branch of the patch explicitly.
06e201c927