Errors when executed over a prepl connection

So this is a bit of a weird onc since there's hardly anyone (possibly just me?) is using prepl for development right now, if you don't care just yet then that's totally fine! Thought I'd let you know anyway :smile:

The error is `Can't change/establish root binding of: *cljs-warnings* with set`, which works fine in a normal REPL. This could be an issue with prepl itself that isn't setting up binding in the right way.

Even if I can't fix it, finding a work around would be great. If I find something I'll put it here, any help would be much appreciated though. This error occurs with any oops operation due to the fact that the setting of `*cljs-warnings*` is attempted by [every macro low down](https://github.com/binaryage/cljs-oops/blob/ad8b3f438d884cb24b533d9f294ebdd2dd2ac91a/src/lib/oops/compiler.clj#L40-L44).

I'm not sure what the difference is between a prepl and regular REPL though. You can try it yourself by starting a prepl:

```
clj -J-Dclojure.server.node="{:port 5556 :accept cljs.server.node/prepl}"
```

Connecting with something like `nc`:

```
nc 127.0.0.1 5556
```

And executing any oops operation such as:

```clojure
(oops.core/ocall #js {"a" +} "a" 1 1)
```