Revert ".git was being touched continuously"

This reverts commit 7855e77e40d626c86d6ae7024d1ffc98c288f0e6.
replace `git status` by `git ls-files ...` to avoid touching .git
Merge pull request #99 from tschottdorf/touch.git

replace `git status` by `git ls-files ...` to avoid touching .git
Merge branch 'master' of https://github.com/magicmonty/bash-git-prompt