locate: more regular file switching
locate: more regular file switching

- don't jump to a module when its cmt is not present (even though we might be
  able to jump directly to the source)
- don't call "move_to" when we're on packs
- stricter [File_switching.t] type

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