Attempt to use upstream js of ocaml

I tried simplifying the build slightly so that

```
opam pin js_of_ocaml git://github.com/ocsigen/js_of_ocaml
make
make install
```

now works.  Unfortunately, the resulting JS no longer actually works :)  I get a

```
ReferenceError: iocaml is not defined (in <long uuid>.js:1)
```

in the IPython frontend.  I couldn't spot any other javascript errors, so I'm at a bit of a loss as to where this ReferenceError is coming from.  Punting it in case it's an easy fix, otherwise I'll hunt it down more tomorrow.