Deploy with classifier does not deploy pom

This is very similar to MINSTALL-41.

Problem is that when there is an classifier set to artifact there is no primary artifact just pom file. Artifact with classifier is placed in attachedArtifacts. It means that it is necessary to deploy POM although there is no primary artifact.

This is fixed by attached patch. There is a new method deploy i a class DeployMojo. This class is subset of same named method of Maven core DefaultArtifactDeployer class. It would be better to change core DefaultArtifactDeployer to ignore null File source argument.