add pdf_stream_filter_callback to lcallbacklib.c 

git-svn-id: https://foundry.supelec.fr/svn/luatex/branches/experimental@5027 0b2b3880-5936-4365-a048-eb17d2e5a6bf
sync with metapost TL 2014

git-svn-id: https://foundry.supelec.fr/svn/luatex/branches/experimental@5028 0b2b3880-5936-4365-a048-eb17d2e5a6bf