Fixes to ChainResolver to handle the proposed maven-integration.

* We do not assume we can magically grab ONE file representing metadata in Chain resolver.
* We add a hook in chain resolver to ignore failure for MavenRepositoryResolver, as this
  resolver, we know, is storing metadata in a maven repo.
* Add a few more debugging messages we'll have to disable before merge.
* Return null when the stale "findyIvyFile" junk is called on a resolver, rather than throwing an exception.