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

diff --cc .gitignore
Simple merge

diff --cc Makefile
Simple merge

diff --cc builtin.h
Simple merge

diff --cc git.c
Simple merge