[MEJB-77] Upgrade maven-archiver to 2.6
 - In accordance with the unit tests i have to fix the
   Stub implementation of MavenProjectBasicStub otherwise
   the tests will fail.


git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1641409 13f79535-47bb-0310-9956-ffa450edef68
Added some comments etc. to make clearer what is meant in the IT's


git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1641427 13f79535-47bb-0310-9956-ffa450edef68