Tone down warnings about reactor dependencies that don't have an associated file

currently this is logged to the WARNING level, but it can be disquieting without causing any real problems. I'm not entirely sure how these messages come up during the clean phase, but at least in the CXF project, they definitely seem to.

We should tone them down to the DEBUG log level for now, unless/until we can find a way of being certain they're going to cause a problem.