Add workaround (and warning message) for when ChainResolver gets a null publication date while we investigate other issues.

* Attempt to set publication date to last modified time, if the stars align
* Issue warning about undefined resolution behavior otherwise
* Add scripted test which exercises the NPE issue in resolving -SNAPSHOTs.
* Commit scalariform style edit in Act.scala

* After parsing and transforming the pom, check for pub date.
* If we don't have a pub date, try to grab lastModified from the URL
* If we can't do anything, issue a warning about the problem artifact.