Add missing "local" before repo_dir & relpath
Rewrote get_repo_files again... :-)

submodules outside home/ are not examined (previously this failed, see https://github.com/andsens/homeshick/issues/108#issuecomment-58442672)
git --recursive leveraged (might need fallback for old git version)
git ls-files is run from the repo root, meaning older git version won't complain any longer
get_repo_dirs, sort and unique are only done once
sort & uniq happen at the same time now (sort -u)
files with newlines in the path are no longer surrounded by quotes
everything is one big pipe like before
code reduced to 23 lines