Ambiguous imports do not fail validation

[dselman]

Ambiguous imports do not fail validation

[mttrbrts]

Here's a similar example that I believe is related.

  const model1 = `
  namespace org.acme
  concept Transaction {}
  `;
  
  const model2 = `
  namespace org.acme.ext
  import org.acme.Transaction
  concept MyTransaction extends Transaction {}`;
  
  let modelFile1 = ParserUtil.newModelFile(modelManager, model1);
  modelManager.addModelFile(modelFile1);
  
  let modelFile2 = ParserUtil.newModelFile(modelManager, model2);
  modelManager.addModelFile(modelFile2);

  modelManager.getType('org.acme.ext.MyTransaction').getSuperType()
      .should.equal('org.acme.Transaction');
  // Fails, actual value is `[email protected]`

[mttrbrts]

Related to #750