Handle git repositories in a single script, vastly simplifying the code

This also correct several error or inconsistencies along the way.

• tar files are no longer recored in git (they lead to very large repositories)

• the code is now serial (since git is serial anyway), so that locking the repo is no longer necessary

• use the flesh's TAR variable instead of looking for tar

• correct paths returned by "find" (git is picky about double slashes)