Merge branch 'lh/git-file'

* lh/git-file:
Teach GIT-VERSION-GEN about the .git file
Teach git-submodule.sh about the .git file
Teach resolve_gitlink_ref() about the .git file
Add platform-independent .git "symlink"

diff --cc cache.h
Simple merge

diff --cc git-submodule.sh
Simple merge

diff --cc refs.c
Simple merge

diff --cc setup.c
Simple merge