Moving field restored for backward compat out into a maven-project specific out into a compat aspect, like the one used in core itself for the plugin manager and lifecycle executor.
maven/components/trunk/maven-project/src/main/aspect/org/apache/maven/project/aspect/compat/
maven/components/trunk/maven-project/src/main/aspect/org/apache/maven/project/aspect/compat/Maven20xProjectCompatAspect.aj