Use git index-pack for much better fetch and clone
Fix locale handling so that gpg and git use the user locale
Use `xgrep` function to always exit grep with success
Fix bug in do_fetch, skip empty line
Fix bugs with gitception://<giturl> related to concurrency with git

Make sure we do not overwrite FETCH_HEAD. Using stacked gitception://
URLs was useful to make sure we handle our temporaries in a safe way.