Merge branch 'bf/fetch-set-head-fix'

Merge branch 'bf/fetch-set-head-fix'

Fetching into a bare repository incorrectly assumed it always used
a mirror layout when deciding to update remote-tracking HEAD, which
has been corrected.

* bf/fetch-set-head-fix:
  fetch set_head: fix non-mirror remotes in bare repositories
  fetch set_head: refactor to use remote directly