Check "classifier" and regular artifact assumption and either handle or detect and report

[cgruber]

The code makes an assumption that deps sections won't have both the main artifact for a group_id/artifact_id pair AND one of the same pom's classified artifacts. It is possible, and in those cases, the deps will be wrong and the build snippet should be explicitly substituted.

We should detect this and report it, or possibly handle it.

[cgruber]

Partial support has happened, under the hood - the underlying library has been updated to support sub-artifacts. This needs a ocnfiguration DSL - probably "classifiers": ["foo"] but it needs care, because we don't want duplicate specification. Need to look at how dependencies add classifiers, and detect that, in order to make sure everything wires up, and then allow this extra download.