It sets up the normal git environment variables and a few helper
functions (currently just "die()"), and returns ok if it all looks like
a git archive. So use it something like
. git-sh-setup-script || die "Not a git archive"
to make the rest of the git scripts more careful and readable.
Fix permissions, and add trivial "reset" and "add" scripts.
The "reset" script just resets the index back to head, while the "add"
script is just a crutch for people used to do "cvs add".
