Revision 618497

[MNG-3119] Modifying MavenProject.addAttachment(..) and MavenProjectHelper.attachArtifact(..) implementations to throw an unchecked exception when a project attachment will collide with existing attachments. This includes tests to verify the behavior. The unchecked exception allows Maven to deal with it as a real build failure, while avoiding the need to modify the MavenProjectHelper API, which is part of Maven's core and which would render many existing plugins incompatible with new Maven releases.