Make it possible to skipp the adding of 'con' classpath entry org.eclipse.jdt.launching.JRE_CONTAINER

It would be nice if it was possible to skip the 'con' classpath entry org.eclipse.jdt.launching.JRE_CONTAINER. For instance, when using WSAD, we typically use a different 'con' classpath entry for the Websphere JRE container instead. Today, I do this by adding it to the maven.eclipse.conclasspath property in project.properties, but this results in duplicate JRE system libraries.