use raise_notrace instead of raise if ocaml version >= 4.02.0

[UnixJunkie]

in case exceptions are used for control flow, we should use faster exception throwing
since the stack trace will never be needed

This is just a proposition. If other maintainers agree, this could be labelled an improvement
and beginner task.

I don't know if this has any benefit for the js_of_ocaml crowds.

[gasche]

Right now, any kind of exceptions is slow on Javascript, I believe. So I suspect that it would work better to just rewrite code to not use exceptions for control flow (I have already done large parts of it in #768 and siblings), and it is not that much work.

[UnixJunkie]

It is maybe not that much work, but I disapprove the fact that idiomatic OCaml code should be rewritten because of the JS crowds.
One should never program anything serious in JS.

[UnixJunkie]

The way forward would be via some preprocessing first.
Then, if alternative versions are contributed (which should not insert performance regressions for regular OCaml users), we could remove the preprocessing hack little by little.