Add testcases for check the results when change the order of with implements/withTraits
minor refactor: adjust recently added utility method
minor refactor: an additional utility method,
Merge pull request #388 from uehaj/master

Add testcases for check the results when change the order of with implem...
minor refactor: improved error message in utility method,
GROOVY-6708: Fix trait inheriting from other generic trait leading to compilation error