Merge branch 'jc/bare'

* jc/bare:
Disallow working directory commands in a bare repository.
git-fetch: allow updating the current branch in a bare repository.
Introduce is_bare_repository() and core.bare configuration variable
Move initialization of log_all_ref_updates

diff --cc cache.h
Simple merge

diff --cc config.c
Simple merge

diff --cc git-am.sh
Simple merge

diff --cc git-checkout.sh
Simple merge

diff --cc git-commit.sh
Simple merge

diff --cc git.c
Simple merge

diff --cc refs.c
Simple merge