o Restored runtime compatibility with plugins that implement custom ArtifactRepositoryLayouts (e.g. appassembler-maven-plugin). The method getId() was added in 3.0 and as such is not implemented by those custom impls. The refactoring done in r1073990 for MNG-4991 eventually made this discrepancy show up during plugin execution.
maven/maven-3/trunk/maven-compat/src/main/java/org/apache/maven/artifact/repository/DefaultArtifactRepository.java