git-fetch fails for tag objects

[talex5]

If we try to test a tag and it isn't in the repository then we use git fetch origin tag/some-tag:git-pull-of-HEAD.new. The intention is to store the tag's head in a new temporary branch.

However, you can't make a branch of a tag object (only of plain tags). The error is:

error: cannot update ref 'refs/heads/git-pull-of-XXX.new': trying to write non-commit object TTT to branch 'refs/heads/git-pull-of-XXX.new'

We should instead pull tags (and maybe everything) to temporary tags, not branches.