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

diff --cc t/t5505-remote.sh
Simple merge

diff --cc t/t5510-fetch.sh
Simple merge