wrong error when imported file ends with expression
mybug.nim:
```nim
let a = @["a", "b", "c"]
echo a
a
```

```
inim
import mybug
/private/tmp/inim_1531877xxx.nim(1, 6) Error: undeclared identifier: 'a'
```

here we probably want to give nim's error un-modified:

mybug.nim(3, 1) Error: expression 'a' is of type 'seq[string]' and has to be discarded
  a
