sync with trunk 4988

git-svn-id: https://foundry.supelec.fr/svn/luatex/branches/experimental@4989 0b2b3880-5936-4365-a048-eb17d2e5a6bf
accessing Lua from metapost

git-svn-id: https://foundry.supelec.fr/svn/luatex/branches/experimental@4990 0b2b3880-5936-4365-a048-eb17d2e5a6bf
fixed wrong lmplib.c mp.w 

git-svn-id: https://foundry.supelec.fr/svn/luatex/branches/experimental@4991 0b2b3880-5936-4365-a048-eb17d2e5a6bf