Merge branch 'jc/lt-ref2-with-lt-refs' into jc/ref-locking

Merge branch 'jc/lt-ref2-with-lt-refs' into jc/ref-locking

* jc/lt-ref2-with-lt-refs:
  Fix show-ref usage for --dereference.
  Document git-show-ref [-s|--hash] option.
  Add man page for git-show-ref
  gitignore: git-show-ref is a generated file.
  Use Linus' show ref in "git-branch.sh".
  Add [-s|--hash] option to Linus' show-ref.
  Teach "git checkout" to use git-show-ref
  Add "git show-ref" builtin command