Problems with relative urls in transformation test cases

[ujhelyiz]

If someone does not have xtuml.common available in the workspace, some test cases do not work as expected:

E.g. in https://github.com/IncQueryLabs/EMDW-MC/blob/master/com.incquerylabs.emdw.cpp.transformation.test/model/HandwrittenComplexModel/model.xtuml the relative references result in platform:/resource/org.eclipse.papyrusrt.xtumlrt.common.model/model/umlPrimitiveTypes.common#... style urls. These urls are resolvable if (1) the xtumlrt.common is installed and the project containing the test cases does not have an Xtext nature, or (2) the xtumlrt.common project is available from the workspace.

I believe, albeit I am not entirely sure that the presence of the Xtext nature result in Xtext loading the resources in an Xtext-provided ResourceSet, that does not use some default URIConverter component the default editors use, thus causing issues.

The Xtext nature might be required for Xtext index to work with the opened UML models, so this issue needs to be looked after.

[abelhegedus]

I believe the test cases should work in an environment where xtumlrt.common is in the target platform, anything else is a plus. Also note that EMF tends to overwrite these references on it's own accord.