Module name clash with prelude leads to cryptic error

I've noticed the following when giving a demo, some students managed to reproduce it.

### Repro

Make a file called `stream.effekt` and put a Hello World inside it:
```scala
def main() = println("hello")
// ERROR: Cannot find a function named `println`.
```

I think this is caused by the implicit [?] module name clashing with the `stream` module in Prelude.