OCaml LLVM tutorial

hi Sarah! I've CC'd the mailing list, which is the right place to send
questions like this :slight_smile: Chris doesn't have much to do with the ocaml
bindings, that's more my thing. Anyway, it looks like you found a bug,
which I've fixed in the trunk. I'll try to get this merged into the
2.7 branch as well. Thanks Sarah!