Pushing all tags with "git push --tags" will also transfer tags from the
tmux-openbsd repository which isn't what we want to do!
Therefore, just specify the newly created tag to push instead for the next
release.
The ours strategy assumes one subsumes the other -- which isn't the case for
the portable version, so for now -- just go back to using the default merge
strategy of recursive, and fix-up any conflicts manually.
