Add a wrapper script as git pre-commit hook

Add a wrapper script as git pre-commit hook

When developer mode is enabled, the wrapper script
"script/git-hooks/pre-commit-hook" gets installed as

  .git/hooks/pre-commit

and calls "script/git-hooks/pre-commit-script".

This way we can later modify the "script/git-hooks/pre-commit-script"
without the need to ever change the installed commit hook itself.

Signed-off-by: Ralph Boehme <slow at samba.org>
Reviewed-by: Martin Schwenke <martin at meltin.net>
Reviewed-by: Jeremy Allison <jra at samba.org>