Merge branch 'np/dreflog'

* np/dreflog:
  show-branch -g: default to the current branch.
  Let git-checkout always drop any detached head
  Enable HEAD@{...} and make it independent from the current branch
  scan reflogs independently from refs
  add reflog when moving HEAD to a new branch
  create_symref(): do not assume pathname from git_path() persists long enough
  add logref support to git-symbolic-ref
  move create_symref() past log_ref_write()
  add reflog entries for HEAD when detached
  enable separate reflog for HEAD
  lock_ref_sha1_basic(): remember the original name of a ref when resolving it
  make reflog filename independent from struct ref_lock