modelVersion. This is required so that a change from modelVersion 4.0.0 to
  4.1.0 doesn't cause compatibility problems with users who have not upgraded
  their projects. It also allows for a certain amount of legacy support into the
  future. Therefore, we should rename this file from pom.xml in the maven-core
  jarfile to pom-4.0.0.xml (and successive revisions to the base pom made to