Inconsistent use of `local import`

[unode]

This was noticed when setting up the motus ngless-contrib module.

The following ngless script runs fine, but I'm not sure it should:

ngless "1.0"
import "motus" version "2.1"

In particular because version 2.1 is not an internal module meaning it should require the local keyword.

Trying to use any of the other modules in ngless-contrib without the local keyword triggers the To import local modules, use "local import" error.

My understanding is that since motus also exists as an internal module (version 1.0) the local keyword check is bypassed.

[unode]

A recent discussion on ngless mailing list reports an error with ngless trying to download motus 2.5 from the official resources website.

Exiting after fatal error while loading and running script
System Error
Could not connect to https://ngless.embl.de/resources/Modules/motus.ngm/2.5.tar.gz (got error code: 404)

Upgrading this report to bug.

The code should validate not just the module name but also that the version is a builtin.