merlin_specific: add raw_compat.mli
merlin_specific: add raw_compat.mli

dra27/merlin,rgrinberg/merlin,rgrinberg/merlin,the-lambda-church/merlin,dra27/merlin,ocaml/merlin,rgrinberg/merlin,the-lambda-church/merlin,the-lambda-church/merlin,dra27/merlin,ocaml/merlin,ocaml/merlin,dra27/merlin,rgrinberg/merlin,ocaml/merlin