[Libreoffice] a few things about ./g, git and git hooks

[Norbert Thiebaud]

I have given the repo translations its own set of git-hooks. that way
the special 'po' handling that was in pre-commit is now only in
translations, and translations' pre-commit does not have
whitespace-checking since this never apply to it.

This triggered changes in ./g to link the git-hooks appropriately.

While I was in ./g I did add ./g -z which allow to do just the
house-keeping on the hooks (and potentially other git house-keeping)

People that are using a 'core' only set-up, and therefore are more
likely to not use ./g that often or at all, should remember to run ./g
-z on occasion.

Norbert