SMP-22 Fail the build if there are duplicate versions already deployed.

This causes a sakai:deploy to fail if there are additional versions of an artifact already deployed. If you want the additional versions to be deleted specify -Dsakai.cleanup=true and it will automatically remove them. The default is false which just warns about them and bails out.

git-svn-id: https://source.sakaiproject.org/svn/maven2/trunk@123950 66ffb92e-73f9-0310-93c1-f5514f145a0a