Excerpts from Martin Langhoff's message of Tue Jan 12 14:33:18 -0500 2010:
So write your own "git-lock" command that does "chmod g-w $@";
git-unlock reenables the group-writable bit. Done.
That was what I was thinking of doing (with modestly more cleverness for
recursive operation), and maybe some convenience flags for git-commit
for automatically unlocking or preserving the lock across a commit.
Cheers,
Edward