sync experimental with trunk

git-svn-id: https://foundry.supelec.fr/svn/luatex/branches/experimental@4743 0b2b3880-5936-4365-a048-eb17d2e5a6bf
sync experimental with trunk

git-svn-id: https://foundry.supelec.fr/svn/luatex/branches/experimental@4745 0b2b3880-5936-4365-a048-eb17d2e5a6bf