creloading a submodule doesn't work

In this code, changes to `SubMod.x` are ignored.
```julia
module TestMod
module SubMod
export x
x = 8
end
using .SubMod
end
```
It's the `using` that's problematic. `SubMod.x` works fine. The proper solution on our side would be to `eval` the submodule code inside the submodule. That's not a trivial amount of work.