GROOVY-6120: VerifyError if field is used in @Category
   * do not allow usage of instance fields or properties in a class annotated with @Category
   * make @Category compatible with @TypeChecked and @CompileStatic
Merge pull request #173 from melix/GROOVY-6120

GROOVY-6120: VerifyError if field is used in @Category
GROOVY-6244: GroovyConsole should display simple messages too